Power transmission system and operation method therefor

ABSTRACT

Between a speed reducing mechanism ( 15, 17, 19 ) for speed-reducing drive power of an electric motor and a differential apparatus ( 7 ) for distributing speed-reduced drive power to axle ends is disposed a clutch ( 5 ) configured for interruptive transmission of drive power.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a power transmission system,such as for an electric automobile using an electric motor as a drivepower source or an electric automobile using a fuel engine (an ordinaryengine making use of an explosion of fuel) and an electric motor both asa drive power source, and to an operation method for the same.

[0003] 2. Description of the Related Art

[0004] There is disclosed in Japanese Patent Application Laid-OpenPublication No. 9-226394 a drive system 2001 for electric automobilesshown in FIG. 22.

[0005] The drive system 2001 for electric automobiles includes anelectric motor 2003, a reduction gear set 2005, and a differentialapparatus 2007.

[0006] The electric motor 2003 is driven by a vehicle-mounted battery toproduce drive power, which is decreased in speed by the reduction gearset 2005 within a range of the number of revolutions of a travellingwheel and increased in torque, and resultant drive power is distributedvia the differential apparatus 2007 to wheels.

[0007] In the drive system 2001, as shown in FIG. 22, the electric motor2003 and the reduction gear set 2005 as well as this reduction gear set2005 and the differential apparatus 2007 are connected directly with noclutch disposed on the way.

[0008] On the other hand, FIG. 23 shows an example of a powertransmission system for a four-wheel driven vehicle having an ordinaryengine as a drive power source.

[0009] This power transmission system includes a transversely arrangedengine 2101, a transmission 2103, a belt-driving transfer 2105, a frontdifferential 2107 (as a differential apparatus for distributing drivepower from the engine 2101 to left and right front wheels), front axles2109 and 2111, left and right front wheels 2113 and 2115, a rear-wheelend propeller shaft 2117, a coupling 2118, a rear differential 2119,rear axles 2121 and 2123, left and right rear wheels 2125 and 2127.

[0010] The drive power from the engine 2101 is transmitted from anoutput gear 2129 of the transmission 2103 via a ring gear 2131 to adifferential case 2133, to be distributed from the front differential2107 via the front axles 2109 and 2111 to the left and right frontwheels 2113 and 2115, or to be transmitted via the differential case2133 m the transfer 2105, and the propeller shaft 2117 to the rear wheelend.

[0011] In this arrangement, the coupling 2118 disposed in a powertransmission subsystem at the rear wheel end is employed for control oftorque transmission to the rear wheels 2125 and 2127.

[0012] For example, when the coupling 2118 is connected, drive powerfrom the engine 2101 is distributed from the rear differential 2119 viathe rear axles 2121 and 2123 to the left and right rear wheels 2125 and2127, rendering the vehicle four-wheel driven.

[0013] When the coupling 2118 is disconnected, the rear differential2119 and subsequent elements of the rear wheel end subsystem are cutoff, rendering the vehicle two-wheel driven.

[0014] In the conventional electric automobiles, an electric motor isconnected directly to wheels, and even in a case of interruption ofpower supply to the electric motor, such as when travelling by inertia,the electric motor is forced to rotate together with wheel rotation,with burdens on the electric motor.

[0015] For example, if the electric motor is a brush type like a DCmotor, brushes receive a great influence on the durability, resulting inincreased maintenance costs, such as by increase in number of servicesfor brush replacement.

[0016] Further, when caused to rotate by wheels, the electric motorserves as a generator, producing electromotive forces (emf). As therotation is increased in speed by the reduction gear set, there isproduced a greater emf, resulting in burdens, such as on a battery oralternator (not shown) or on circuit elements such as a regulatorconstituted as an integrated circuit, causing a reduced durability.

SUMMARY OF THE INVENTION

[0017] The present invention is made with such points in view. Ittherefore is an object of the present invention to provide a powertransmission system with a compact size, light weight, and welladaptation for vehicle-mounting, preventing an electric motor from beingcaused to rotate by rotation of wheels, and an operation method for thesame.

[0018] To achieve the object, according to a 1^(st) aspect of theinvention, there is provided a power transmission system comprising aspeed reducing mechanism for speed-reducing drive power of an electricmotor, a differential apparatus for distributing speed-reduced drivepower to axle ends, and a clutch configured for interruptivetransmission of drive power between the speed-reducing mechanism and thedifferential apparatus.

[0019] Accordingly, in case power supply to the electric motor isinterrupted, such as when travelling by inertia, connection of theclutch is canceled, thereby disconnecting the electric motor fromwheels.

[0020] Thus, the electric motor is set free from being rotated byrotation of the wheels, and kept from generating emf that otherwisemight have imposed loads on a battery, alternator, or controller'scircuit elements, allowing these to have maintained performances, with agreatly improved durability.

[0021] Because mechanical rotation is prevented, burdens on andtemperature rise of magnetic field or rotor side windings of theelectric motor are reduced, as well as burdens on bearings, with agreatly improved durability.

[0022] In case of a brush type electric motor, such as a DC motor, thebrushes have greatly improved durability, with a commensurate reductionin frequency of their replacement, with reduction of maintenance cost.

[0023] According to a 2^(nd) aspect second aspect of the invention, apower transmission system according to the 1^(st) aspect furthercomprises a main drive power source, and the electric motor used as anauxiliary drive power source relative to the main drive power source.

[0024] Accordingly, in a four-wheel driven vehicle using both a maindrive power source (engine) and an electric motor, when the electricmotor is rotated with the clutch in connection, the vehicle enters afour-wheel driven state with improvements such as in abilities of start,acceleration, and riding performances such as on differences in level orcavities in road.

[0025] In a two-wheel driven travel at the engine side, or uponoccurrence of a rollback by front wheels idling such as on an inclinedroad low of surface frictional resistance in a four-wheel driven travel,the clutch is disconnected to interrupt connection between the electricmotor and wheels, whereby the electric motor is kept from being rotatedby rotation of wheels, allowing for like effects to the 1^(st) aspect tobe achieved.

[0026] According to a 3^(rd) aspect of the invention, in a powertransmission system according to the 1^(st) or 2^(nd) aspect, thespeed-reducing mechanism comprises a plurality of reduction gear setsincluding a first reduction gear set for inputting thereto drive powerfrom the electric motor, the first reduction gear set comprising aplanetary gear, whereby like effects to the 1^(st) or 2^(nd) aspect areachieved.

[0027] In addition, by use of the planetary gear in the first reductiongear set, the speed-reducing mechanism which is constituted with aplurality of stages can be made small in size.

[0028] In particular, in the case the electric motor is used as anauxiliary drive power source relative to the main drive power source,the input from the electric motor to the speed-reducing mechanism is hasa smaller value than a case the electric motor is used as a main drivepower source, and the arrangement in which the first reduction gear setis constituted with the planetary gear allows an efficient reduction insize of the speed-reducing mechanism.

[0029] According to a 4^(th) aspect of the invention, in a powertransmission system according to the 3^(rd) aspect, the speed-reducingmechanism is provided with an oil pump for supplying lubricant to theplanetary gear, whereby like effects to the 3^(rd) aspect can beachieved, in addition to effective lubrication of the planetary gear,possible reduction of meshing resistance of the planetary gear, andpreventive gnaw of gears.

[0030] According to a 5^(th) aspect of the invention, in a powertransmission system according to the 4^(th) aspect, the oil pump isprovided on a lid side of a case, whereby like effects to the 4^(th)aspect can be achieved.

[0031] In addition, oil pump can be machined and mounted with ease, anda lid part of the case can be used as part of the oil pump to constitutean tight-closed part, with a simplified structure.

[0032] According to a 6^(th) aspect of the invention, in a powertransmission system according to any of the 1^(st) to 5^(th) aspects,the speed-reducing mechanism comprises a plurality of reduction gearsets, and the clutch is disposed in a power transmission path of thespeed-reducing mechanism, whereby like effects to the 1^(st) to 5^(th)aspects can be achieved.

[0033] In addition, this arrangement in which the clutch is disposed ina power transmission path of the speed-reducing mechanism allows, forexample, a selected clutch to be disposed in a place optimal of speedreduction ratio in accordance with the type and capacity, or an optimalclutch to be selected in accordance with sliding speed or transmittingtorque of reduction gears, and the like.

[0034] Like this, flexibility of design can be increased with respect tothe place for disposition of the clutch, as well as to the clutchselection.

[0035] According to a 7^(th) aspect of the invention, in a powertransmission system according to the 6^(th) aspect, the speed-reducingmechanism and the differential apparatus are neighbored to each other,and the clutch is coaxially provided to one of the plurality ofreduction gear sets of the speed-reducing mechanism that is nearest tothe differential apparatus, whereby like effects to the 6^(th) aspectcan be achieved.

[0036] In addition, because the clutch is coaxial to one of reductiongear sets of the speed-reducing mechanism that is nearest to thedifferential apparatus, the clutch can be arranged within a projectionarea of large-size parts, such as a ring gear of the differentialapparatus, allowing the system to be entirely compact in size.

[0037] According to an 8^(th) aspect of the invention, in a powertransmission system according to any of the 1^(st) to 7^(th) aspects,the speed-reducing mechanism and the differential apparatus areintegrally arranged in a casing, whereby like effects to the 1^(st) to7^(th) aspects can be achieved.

[0038] In addition, because the clutch is integrated with thespeed-reducing mechanism and the differential apparatus, the powertransmission system can be the more light-weighted, compact in size, andimproved in vehicle-mountability.

[0039] Further, since the speed-reducing mechanism is integrated withthe differential apparatus, the amount of oil to be supplied to theclutch is increased, allowing sufficient lubrication and cooling, andgreatly improved durability, permitting a normal use to be near 100-%capacity.

[0040] Along therewith, the clutch can be made smaller in size, allowingthe power transmission system to be the more light-weighted and compactin size.

[0041] According to a 9^(th) aspect of the invention, in a powertransmission system according to the 8^(th) aspect, a final reductiongear set and a previous reduction gear set relative thereto are axiallyneighbored to each other, whereby like effects to the 8^(th) aspect canbe achieved.

[0042] In addition, reduction gear can have a shorter support span,allowing adequate meshing of the gear, reduced vibration, and enhanceddurability.

[0043] According to a 10^(th) aspect of the invention, in a powertransmission system according to the 9^(th) aspect, the previousreduction gear set is disposed on an axially one side of the finalreduction gear set, and the differential apparatus is disposed on anaxially opposite side of the final reduction gear set, whereby likeeffects to the 9^(th) aspect can be achieved.

[0044] In addition, the casing which has the final reduction gear andthe differential apparatus incorporated therein can have a controlledweight balance in a vehicle-transverse direction.

[0045] According to an 11^(th) aspect of the invention, in a powertransmission system according to the 10^(th) aspect, the clutch iscoaxially neighbored, at an axially outer side, to the differentialapparatus, whereby like effects to the 10^(th) aspect can be achieved.

[0046] In addition, the casing can have a controlled weight balance in avehicle-longitudinal direction also. Further, for the clutch to be sethardly receives restriction due to interference with peripheral members,flexibility of design is enhanced, such as in clutch capacity, clutchconfiguration, and condition for installation of an actuator.

[0047] According to a 12^(th) aspect of the invention, in a powertransmission system according to the 7^(th) or 8^(th) aspect, theplurality of reduction gear sets of the speed-reducing mechanism isprovided near a differential center of the differential apparatus,whereby like effects to the 7^(th) or 8^(th) aspect can be achieved.

[0048] In addition, because the reduction gear sets are arranged nearthe differential center of the differential apparatus, an entirety ofpower transmission system including the differential apparatus and thespeed-reducing mechanism can be well-balanced.

[0049] In particular, in case the differential apparatus and thespeed-reducing mechanism are separately fabricated and disposed to beadjacent with each other, a joint part between the differentialapparatus and the speed-reducing mechanism is free from undue extraforces, as an advantage in strength, as well.

[0050] According to a 13^(th) aspect of the invention, in a powertransmission system according to any of the 1^(st) to 8^(th) and 12^(th)aspects, the clutch comprises a frictional clutch, whereby like effectsto the 1^(st) to 8^(th) and 12^(th) aspects can be achieved.

[0051] In addition, this arrangement of power transmission system isallowed to arbitrarily control transmission torque by regulatingpressing forces of the frictional clutch.

[0052] Further, the use of a frictional clutch eliminates generation ofratchet sounds such as in meshing clutch for example, and high ofcalmness.

[0053] The use of a frictional clutch eliminates shocks and shock soundsin clutch connection and cancellation thereof.

[0054] The frictional clutch does not need synchronization of rotationin clutch connection and cancellation thereof, and can be fabricated atthe lower cost.

[0055] According to a 14^(th) aspect of the invention, in a powertransmission system according to the 13^(th) aspect, the frictionalclutch comprises a multi-plate clutch, whereby like effects to the13^(th) aspect can be achieved.

[0056] In addition, this arrangement of power transmission system usinga multi-plate clutch is allowed to handle large drive power, because themulti-plate clutch can use wide frictional surface areas to obtain asufficient capacity even if compact in size.

[0057] Moreover, by making the multi-plate clutch compact, the powertransmission system can be the more light-weighted, compact in size, andimproved in vehicle-mountability.

[0058] Further, because the clutch plates can be easily changed innumber and diameter to thereby adjust the capacity, there is greatflexibility in design.

[0059] According to a 15^(th) aspect of the invention, in a powertransmission system according to the 13^(th) aspect, the frictionalclutch comprises a cone clutch, whereby like effects to the 13^(th)aspect can be achieved.

[0060] In addition, because the cone clutch is simple in structure andsmall of components, the power transmission system can be the morelight-weighted, compact in size, improved in vehicle-mountability, andreduced in cost.

[0061] According to a 16^(th) aspect of the invention, in a powertransmission system according to any of the 1^(st) to 8^(th) and 12^(th)aspects, the clutch comprises a meshing clutch, whereby like effects tothe 1^(st) to 8^(th) and 12^(th) aspects can be achieved.

[0062] In addition, because the meshing clutch is free from draggingtorque due such as to viscosity of oil, unlike the frictional clutches,the loss of drive power is little, allowing for the electric motor to beimproved in durability.

[0063] Because of unnecessary countermeasures such as lowering oilviscosity, raising temperature, and reducing amount of oil for thedragging torque to be reduced, implementation can be the more reduced incost.

[0064] Moreover, when the clutch is disconnected, the electric motor isnot mechanically rotated by dragging torque, protection performancessuch as of a battery, alternator, and circuit elements can be improved,as well as durability of the electric motor.

[0065] Further, this arrangement of power transmission system employs ameshing clutch which can provide a compact size with a great capacity,allowing for great drive power to be handled.

[0066] Still more, because the meshing clutch is simple in structure andsmall of component number, the power transmission system can be the morelight-weighted, compact in size, and improved in vehicle-mountability,with a low cost.

[0067] According to a 17^(th) aspect of the invention, in a powertransmission system according to the 16^(th) aspect, the meshing clutchcomprises a dog clutch, whereby like effects to the 16^(th) aspect canbe achieved.

[0068] In addition, because the dog clutch does not need connectionmembers such as coupling sleeve to be moved between meshing teeth forengagement or disengagement, the structure is by far simple and low ofcost. Moreover, as a narrow installation space can do, this arrangementof power transmission system is allowed to have a clutch portion themore simplified in structure, reduced in cost, and compact in size.

[0069] According to an 18^(th) aspect of the invention, in a powertransmission system according to any of the 1^(st) to 8^(th) and 12^(th)aspects, the clutch comprises a one-way clutch, whereby like effects tothe 1st to 8^(th) and 12^(th) aspects can be achieved.

[0070] In addition, when connection is canceled, the one-way clutch isfree from rotational resistance such as by dragging torque in frictionalclutch, and in this arrangement of power transmission system using aone-way clutch, the electric motor in a stopped state is prevented frombeing rotated, with the more improved durability.

[0071] Because the one-way clutch does not need an operation mechanismnor control mechanism therefor, the above arrangement of powertransmission system is the more simplified, light-weighted, and compactin size.

[0072] By use of a small-sized lightweight one-way clutch, the abovearrangement of power transmission system can be more light-weighted andcompact.

[0073] Further, in application such as to a four-wheel driven electricautomobile using an electric motor as an auxiliary drive power source,the one-way clutch may be arranged to be connected when the vehicle runsforward, so that upon rotation of the electric motor associated wheelsare driven via the one-way clutch, allowing for the vehicle to haveimproved abilities such as when starting or in acceleration, or to runover differences in level, cavities in road, etc.

[0074] Still more, when rotation of the electric motor is stopped, thevehicle enters a two-wheel driven state. In this state, connection ofthe one-way clutch is canceled by preceding rotation of associatedwheels, of which rotating actions otherwise might have forced theelectric motor to rotate, but now are isolated from the electric motor.

[0075] Like this, the electric motor is prevented against such forcedrotation, to be free from burdens that otherwise might have been imposedto produce emf, such as on a battery, alternator, circuit elements,etc., and is allowed to have an enhanced durability.

[0076] According to a 19^(th) aspect of the invention, in a powertransmission system according to any of the 1^(st) to 8^(th) and 12^(th)aspects, the clutch comprises a two-way clutch in which cancelingdirections of relative rotations are switchable, whereby like effects tothe 1^(st) to 8^(th) and 12^(th) aspects can be achieved.

[0077] In addition, in this arrangement of power transmission systemusing a two-way clutch, the electric motor can be prevented from beingforced to rotate by wheels, in both forward run and backward run.

[0078] Therefore, it can cope with a rollback of the vehicle, allowingfor enhanced protection to be effected, such as of the electric motor, abattery, an alternator, associated circuit elements, etc.

[0079] Unlike the case of using a one-way clutch that needs anotherclutch for backward run and an extra controller for necessary connectionin the backward run and disconnection for forward run, the abovearrangement of power transmission system using a two-way clutch, copingalso with backward run as described, does not need the clutch forbackward run nor the extra controller, and is allowed to be the moresimplified in structure, light-weighted, compact, and improved invehicle-mountability, with a low cost.

[0080] Further, this arrangement of power transmission system has likeeffects to the 18^(th) aspect using a one-way clutch.

[0081] According to a 20^(th) aspect of the invention, in a powertransmission system according to any of the 1^(st) to 8^(th) and 12^(th)aspects, the clutch comprises a centrifugal clutch, whereby like effectsto the 1^(st) to 8^(th) and 12^(th) aspects can be achieved.

[0082] In a four-wheel driven electric automobile employing both a maindrive power source (engine) and an electric motor, the centrifugalclutch is disposed on a driving end, and the electric motor iscontrolled so as to start when the centrifugal clutch is connected.

[0083] When the vehicle is stopped (to start) or when the vehicle speedis decreased so that wheel revolution speed becomes lower than acritical value, the centrifugal clutch is connected, and the electricmotor is started, driving wheels via the centrifugal clutch, renderingthe vehicle four-wheel driven.

[0084] If the vehicle speed is increased so that the wheel revolutionspeed reaches critical value, the centrifugal clutch is operated forclutch cancellation, when rotation of the electric motor is stopped torender the vehicle two-wheel driven from the engine.

[0085] Like this, because forced rotation by the vehicle is isolatedfrom the electric motor by use of the centrifugal clutch, the electricmotor is prevented against such forced rotation, to be free from burdensthat otherwise might have been imposed to produce emf, such as on abattery, alternator, circuit elements, etc., and is allowed to have anenhanced durability.

[0086] In addition, when the connection is cancelled, as the centrifugalclutch is free from rotational resistance unlike the frictional clutchsubjected to dragging torque, the above arrangement of powertransmission system using a centrifugal clutch have the more improvedeffects, such as on fuel consumption (when two-wheel driven) withrotation of the electric motor stopped, or on durability of the motor.

[0087] In addition, in this arrangement of power transmission systemusing a centrifugal clutch, the electric motor can be kept from beingforced to rotate by wheels, in both forward run and backward run,permitting effective protection such as of battery, alternator, andcircuit elements.

[0088] Because the centrifugal clutch does not need an operationmechanism nor control mechanism therefor, the above arrangement of powertransmission system is the more simplified, light-weighted, and compactin size.

[0089] By use of a small-sized lightweight centrifugal clutch, the abovearrangement of power transmission system can be more light-weighted andcompact, allowing for great drive power to be handled.

[0090] Further, to achieve the object described, according a 21^(st)aspect of the invention, there is provided an operation method for apower transmission system according to any of the 16^(th) to 20^(th)aspects, the method comprising the step of canceling connection of theclutch, switching a rotating direction of the electric motor, therebycausing a contact portion of the clutch to vibrate so that the contactportion has a reduced frictional resistance.

[0091] Like this, when canceling connection of the clutch, the directionof rotation of the electric motor is switched to give vibration to acontact portion of the clutch so that the contact portion has a reducedfrictional resistance, thereby allowing connection and cancellation,such as of a meshing clutch, one-way clutch, two-way clutch, orcentrifugal clutch, to be properly effected, when intended, or at apredetermined vehicle speed.

[0092] Like this, there can be maintained protection functions to behigh, such as of an electric motor, battery, alternator, and circuitelements in a power transmission system according to any of the 16^(th)to 20^(th) aspects.

[0093] Further, a four-wheel driven state of the vehicle can be changedto a two-wheel driven state, as necessary, with enhancedmaneuverability.

[0094] According to a 22^(nd) aspect of the invention, there is providedan operation method for a power transmission system according to any ofthe 16^(th) to 20^(th) aspects, the method comprising the step ofcanceling connection of the clutch, changing a revolution number of theelectric motor so that a contact portion thereof has a reducedfrictional resistance, whereby like effects to the 21^(st) aspect can beachieved.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0095] The above and further objects and novel features of the presentinvention will more fully appear from the following detailed descriptionwhen the same is read in conjunction with the accompanying drawings, inwhich:

[0096]FIG. 1 is a sectional view of an essential portion of a powertrain system including a power transmission system according to a firstembodiment of the invention;

[0097]FIG. 2 is a skeleton diagram of the power train system;

[0098]FIG. 3 is a sectional view of an essential portion of a powertrain system including a power transmission system according to a secondembodiment of the invention;

[0099]FIG. 4 is a sectional view of an essential portion of a powertrain system including a power transmission system according to a thirdembodiment of the invention;

[0100]FIG. 21 is a sectional view of an essential portion of a powertrain system including a power transmission system according to afourteenth embodiment of the invention;

[0101]FIG. 22 is a sectional view of an essential portion of aconventional power train system including a power transmission system;and

[0102]FIG. 23 is a skeleton diagram of the conventional power trainsystem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0103] There will be detailed below 14 preferred embodiments of thepresent invention with reference to the accompanying drawings. Likemembers are designated by like reference characters.

[0104] In the embodiments, the term “differential center” means a middleposition of a differential apparatus between left and right meshingparts at which left and right output gears (side gears) engage with leftand right output shafts, respectively. For example, in the case of adifferential apparatus using a bevel gear, the differential center islocated on a shaft axis center of pinion shafts, that is a center pointof pinion shafts in a rotation shaft direction of the differentialapparatus.

[0105] It is noted that in the drawings, sectional views representsections along planes intersecting at an angle. It may be necessary fora casing to be compact in size to position a later-described secondshaft at an even or higher level to or than a differential shaft, whilea later-described first shaft and electric motor may well be locatedlower. The casing has lubricant oil filled to a sufficient level for thesecond shaft to be well lubricated.

First Embodiment

[0106]FIG. 1 and FIG. 2 show a transmission system 1 of drive power ofan electric motor according to the first embodiment of the invention.

[0107] The power transmission system 1 has features of the 1^(st),2^(nd), 6^(th), 7^(th), 8^(th), 12^(th), 13^(th), and 14^(th) aspects ofthe invention. Note the terms “transverse”, “left” and “right” meanthose of a vehicle equipped with the power transmission system 1, andthose in FIG. 1.

[0108] The power transmission system 1 is configured to be arranged on arear wheel side of a four wheel driven vehicle using an engine and anelectric motor, such as an electric automobile shown in FIG. 2, forexample.

[0109] This vehicle is equipped with a power train system which has: afront-wheel side power train including a transversely arranged engine2101, a transmission 2103, a front differential 2107 (as a differentialapparatus for distributing drive power of the engine 2101 to left andright front wheels), left and right front axles 2109 and 2111, and leftand right front wheels 2113 and 2115; and a rear-wheel side power trainincluding a sensor 2135 for detecting necessary data, a controller 2133responsible for data input from the sensor 2135 to provide necessarycontrol commands, an electric motor 2129 controlled with a controlcommand of the controller 2133 to provide drive torque, a battery 2131as a secondary cell for supplying electric power to the motor 2129, aspeed-reducing mechanism 3 connected to the motor 2129, a reardifferential 7 connected via left and right rear axles 2121 and 2123 toleft and right rear wheels 2125 and 2127, and an on-off clutch 5responsible for another command of the controller 2133 to be engaged anddisengaged for interconnection between the speed-reducing mechanism 3and the rear differential 7.

[0110] The sensor 2135 may detect data on an rpm of the eigine 2101, atravelling speed of the vehicle, and an rpm of some wheel to therebycalculate a slip of the wheel, and the controller 2133 may beresponsible for any of an excessive slip and manual commands from adriver to select an adequate control command.

[0111] For normal run, the front wheels 2113 and 2115 are always drivenfrom the engine 2101, and when necessary, the rear wheels 2125 and 2127are auxiliary driven from the electric motor 2129.

[0112] Structure of the power transmission system 1 will then bedetailed with reference to FIG. 1.

[0113] The power transmission system 1 is constituted with thespeed-reducing mechanism 3, the on-off clutch 5 (as a clutch) to beelectromagnetically controlled, the rear differential 7 (as adifferential apparatus), the controller 2133, etc.

[0114] The power transmission system 1 is accommodated in a casing 9,which is constituted as a combination of a gear casing part 11 foraccommodating the speed-reducing mechanism 3 and the on-off clutch 5,and a differential carrier part 13 for accommodating the reardifferential 7.

[0115] The casing 9 is provided with an oil sump.

[0116] The speed-reducing mechanism 3 is constituted with a first shaft33, a second shaft 35, and a third shaft (37+39), which are providedwith three stages of reduction gear sets 15, 17, and 19.

[0117] The third shaft is a combination of mutually coaxially arrangedouter and inner shafts 37 and 39.

[0118] The reduction gear set 15 is a combination of reduction gears 21and 23. The reduction gear set 17 is a combination of reduction gears 25and 27. The reduction gear set 19 is a combination of reduction gears 29and 31.

[0119] More specifically, one reduction gear 21 of the reduction gearset 15 is formed on an axially central part of the first shaft 33, andthe other reduction gear 23 of the gear set 15 is formed on a right partof the second shaft 35.

[0120] One reduction gear 25 of the reduction gear set 17 is formed on aleft part of the second shaft 35, and the other reduction gear 27 of thegear set 17 is formed (as a drive power transmitting member) on theouter shaft 37 of a hollowed configuration.

[0121] One reduction gear 29 of the reduction gear set 19 is formed (asa drive power transmitting member) on a right part of the inner shaft39. The other reduction gear 31 of the gear set 19 is configured as aring gear to be fixed by bolts 43 to a differential casing 41 of therear differential 7.

[0122] Like this, the reduction gear sets 15, 17, and 19 have astaggered structure, whereby they can be disposed near a plane centeredto the rear differential 7. The first shaft 33 is supported at its leftend and central part by the gear casing part 11 via left and right ballbearings 45 and 47 respectively interposed therebetween, and isoperatively connected at its right end to an output shaft of therear-wheel driving electric motor 2129. Between the first shaft 33 andthe gear casing part 11 is disposed an oil seal 49 for prevention of oilleakage to the outside.

[0123] The second shaft 35 is supported at its central part and rightend by the gear casing part 11 via left and right ball bearings 51 and53 respectively interposed therebetween.

[0124] In this embodiment, the left ball bearing 51 is not located on aleft end of the second shaft 35, but on the central part, therebyallowing for the left end to be configured as an engagement partrelative to the outer shaft 37.

[0125] The inner shaft 39 of the third shaft is supported at its leftand right ends by the gear casing part 11 via left and right bearings 55and 57 respectively interposed therebetween. The outer shaft 37 issupported at its left end and central part by an outer periphery of theinner shaft 39 via left and right bearings 59 and 61 respectivelyinterposed therebetween.

[0126] The differential case 41 is supported at its left and right endsby the differential carrier part 13 via left and right bearings 63 and65 respectively interposed therebetween.

[0127] Like above-mentioned, the reduction gear set 19 includes (as thereduction gar 31) the ring gear on the rear differential 7 side, andfurther the reduction gear sets 15, 17, and 19 are accommodated in thesame casing 9. The reduction gear sets 15, 17, and 19 are thusintegrated with the rear differential 7, to be a unit.

[0128] The on-off clutch 5 is disposed between the outer shaft 37 andthe inner shaft 39. When the clutch 5 is engaged for interconnection,drive power of the electric motor 2129 is transmitted, via the reductiongear sets 15, 17, ad 19, where its speed is reduced in a three-stagedmanner, to the differential case 41 of the rear differential 7 to bethereby rotated.

[0129] The rear differential 7 has a bevel gear type differentialmechanism, which is constituted with a plurality of pinion shafts fixedto the differential casing 41, a plurality of pinion gears individuallysupported by the pinion shafts, and a pair of torque outputting left andright side gears meshing with the pinion gears.

[0130] The left and right side gears are splined on the left and rightrear axles 67 and 69, which transversely extend through the differentialcarrier part 13, to be externally connected via left and right joints 71and 73 to the left and right rear wheels 2125 and 2127.

[0131] Between each rear axle 67 or 69 and the differential carrier part13 is disposed an oil seal 75 for prevention of oil leakage to theoutside.

[0132] As the electric motor 2129 rotates, drive power therefrom isinput to the differential case 41, wherefrom it is distributed via thepinion shafts and the pinion gears to the left and right side gears, andfurther via the left and right rear axles 67 and 69 to the left andright rear wheels 2125 and 2127, rendering the vehicle four-wheeldriven, with enhanced abilities such as for bad-road escape and travel,start, acceleration, and vehicle body stabilization.

[0133] If a difference develop between rear wheel drive resistances suchas on a bad road, the pinion gears individually revolve to effect adifferential distribution of drive power to the left and right rearwheels 2125 and 2127.

[0134] When rotation of the electric motor 2129 is stopped, the vehicleenters a two-wheel driven state with the front wheels 2113 and 2115driven from the engine 2101, where the controller 2133 cancelsengagement of the on-off clutch 5, thereby interrupting theinterconnection between the electric motor 2129 and the rear wheels 2125and 2127.

[0135] The on-off clutch 5 is constituted with a rotary case 77, a mainclutch 79 as a multi-plate frictional clutch, a multi-plate pilot clutch81, a ball cam 83, a cam ring 85, a pressure plate 87, an armature 89,an electric magnet 91, and a trochoid gear pump 93, and controlled fromthe controller 2133.

[0136] The rotary case 77 is welded to the outer shaft 37 of thereduction gear set 19, and the main clutch 79 is arranged between therotary case 77 and the inner shaft 39 of the reduction gear set 19.

[0137] The pilot clutch 81 is arranged between the rotary case 77 andthe cam ring 85.

[0138] The ball cam 83 is formed between the cam ring 85 and thepressure plate 87. The rotary case 77 has a left wall part as a rotor 95of a magnetic material constituting part of a magnetic flux circuit ofthe magnet 91. The rotor 95 is supported by needle bearings 97 arrangedon the inner shaft 39.

[0139] Between the cam ring 85 and the rotor 95 is disposed a thrustbearing 99 receiving a cam reaction force of the ball cam 83, as well asa washer.

[0140] The pressure plate 87 is relatively movably connected to theinner shaft 39.

[0141] The armature 89 is axially movably disposed between the pilotclutch 81 and the pressure plate 87, and is axially positioned by a stopring.

[0142] The magnet 91 has a core 101 connected to the gear casing part 11by a connection member 103 and a bolt 105, and lead wires 109 drawn outfrom a coil 107 via the core 101 and the gear casing part 11, to beexternally connected to the battery 2131 of the vehicle.

[0143] Between the core 101 and the rotor 95 is provided an air gap. Therotor 95 is radially divided with stainless steel rings to therebyconstitute part of the magnetic flux circuit of the magnet 91.

[0144] The controller 2133 is adapted for excitation of the magnet 91,control of exciting current, cease of excitation, etc.

[0145] The controller 2133 is further adapted to control the rear-wheeldriving electric motor 2129 to start and stop rotation. When rotation ofthe electric motor 2129 is stopped, excitation of the magnet 91 also isstopped.

[0146] When the magnet 91 is excited, the armature 89 is attracted,pressing the pilot clutch 81 to engage.

[0147] As the pilot clutch 81 is engaged, torque to be transmittedbetween the reduction gear sets 17 and 19 is imposed on the ball cam 83,via the cam ring 85 connected by the pilot clutch 81 to the rotary case77 and the pressure plate 87 connected to the inner shaft 39. There isgenerated a cam thrust force, which is received by the pressure plate87, which is thus forced to move rightward, pressing the main clutch 79to engage.

[0148] When the on-off clutch 5 is thus connected, drive power of theelectric motor 2129 is transmitted through the reduction gear sets 15,17, and 19, to the rear differential 7, rendering the vehicle four-wheeldriven.

[0149] As the exciting current of the magnet 91 is controlled, the pilotclutch 81 has a commensurate slip, changing the cam thrust force of theball cam 83, causing the main clutch 79 to have a varied connectionforce, thereby controlling drive power to be transmitted from theelectric motor 2129 to the rear wheel ends.

[0150] Such control of drive power can be effected while the vehicle isturning, with enhanced turnability and increased stability of thevehicle body.

[0151] When the excitation of the magnet 91 is stopped, the pilot clutch81 is released, causing the ball cam 83 to lose cam thrust force, andthe main clutch 79 is released, canceling connection of the on-offclutch 5, thereby rendering the vehicle two-wheel driven.

[0152] The controller 2133 is adapted, when the vehicle starts, torotate the electric motor 2129 and concurrently make the on-off clutch 5connected, causing the vehicle to enter a four-wheel driven state, whereit has increased drive power due to cooperation of the engine 2101 andthe electric motor 2129, with enhanced starting and acceleratingabilities.

[0153] When a specified vehicle speed (for example, 20 km/h) is reached,the controller 2133 stops rotation of the electric motor 2129,concurrently canceling connection of the on-off clutch 5, causing thevehicle to enter a two-wheel driven state.

[0154] Further, the controller 2133 is adapted, also when going up aslope, to render the vehicle four-wheel driven to have increased drivepower.

[0155] While going up the slope, if the vehicle suffers a roll backcondition in which the front wheels 2113 and 2115 idle so that thevehicle retreats, the controller 2133 stops rotation of the electricmotor 2129 and cancels connection of the on-off clutch 5.

[0156] Like this, when connection of the on-off clutch 5 is canceled,the electric motor 2129 is cut off from the rear wheels 2125 and 2127,to be free from forced rotation due to rotation of the rear wheels (in aforward direction when going ahead, or in a reverse direction whenrolling back).

[0157] When increased drive torque is desirable, while travelling,irrespective of the specified vehicle speed after the start of vehicle,the controller 2133 may be controlled to rotate the electric motor 2129and connect the on-off clutch 5, to have an increased ability to runover a difference in level or cavity or depression in a road, with stillenhanced accelerating ability.

[0158] The trochoid gear pump 93 is driven for rotation by the innershaft 39 via a hollow connection shaft 111, to pump up oil from the oilsump of the casing 9, and to supply pumped oil through axial and radialoil paths formed in the connection shaft 111 and the inner shaft 39 tothe main clutch 79, pilot clutch 81, ball cam 83, thrust bearing 99, andthe like, making sufficient lubrication and cooling thereto.

[0159] The coil 107 of the magnet 91 also is cooled by oil, having astabilized performance, while the heat warms oil in the oil sump, aswell as the pilot clutch 81 and the ball cam 83 therearound, and warmedoil is sent from the gear box 93 to the main clutch 79 and the like,warming them.

[0160] The power transmission system 1 of the electric motor 2129 isthus constructed.

[0161] In the power transmission system 1, when the vehicle is two-wheeldriven or suffering a rollback, the electric motor 2129 is disconnectedfrom the rear wheels by the on-off clutch 5, preventing generation ofemf that otherwise might have imposed great loads such as on thebattery, alternator, associated circuit elements, etc.

[0162] These elements thus have their functions maintained to beadequate, with improved durability.

[0163] The electric motor 2129 is not forced to rotate by rotation ofthe rear wheels, whereby the burden on, as well as the temperature riseof, magnetic field or rotator side windings and burdens on the bearingsare reduced, with improved durability of the electric motor 2129.

[0164] As brushes of the electric motor 2129 have a greatly increaseddurability, their replacement can do with a commensurate decrease infrequency, resulting in a great decrease of maintenance cost.

[0165] The on-off clutch 5 is disposed between the reduction gear sets17 and 19, whereby the on-off clutch 5 is integrated with thespeed-reducing mechanism, resulting in a commensurate light-weighting,compact size, and vehicle-mountability of the power transmission system1.

[0166] Components of the on-off clutch 5, such as the main clutch 79,pilot clutch 81, and ball cam 83 are sufficiently lubricated and cooledby forced lubrication by the gear pump 93, to have a greatly improveddurability, allowing for a use near 100-% capacity.

[0167] The on-off clutch 5 is thus allowed to be smaller in size,permitting the power transmission system 1 to be the more light-weightedand compact.

[0168] The arrangement with the on-off clutch 5 provided in thespeed-reducing mechanism allows, for example, a selected on-off clutch 5to be disposed in an optimal place selective from among the reductiongear sets 15, 17, and 19 in accordance with the type and capacity, or anoptimal on-off clutch to be selected in accordance with given conditionssuch as a sliding speed and transmitting torque of the reduction gearset 15, 17, or 19.

[0169] Like this, for the on-off clutch 5, flexibility of design isgreatly increased with respect to the clutch location and selection.

[0170] The reduction gear sets 15, 17, and 19 and the rear differential7 are installed as a unit in the casing 9, thereby allowing the powertransmission system 1 to be the more light-weighted, compact in size,and improved in vehicle-mountability.

[0171] By this unitizing, a volume of oil sealed in the casing 9 can bewholly supplied to the on-off clutch 5, with increase in amount ofcirculating oil, allowing for the on-off clutch 5 to have greatlyenhanced lubrication and cooling effects.

[0172] Because the reduction gear sets 15, 17, and 19 are arranged nearthe differential center of the differential apparatus 7, an entirety ofpower transmission system including the differential apparatus 7 and thespeed-reducing mechanism 3 can be well-balanced.

[0173] In particular, a connection portion (or joint parts whenseparately formed and disposed adjacent to each other) between thedifferential apparatus 7 and the speed-reducing mechanism 3 is free fromundue extra forces, as an advantage in strength, as well.

[0174] In addition, the power transmission system 1 using a multi-platemain clutch 79 (as a frictional clutch) is allowed to arbitrarilycontrol drive torque of the electric motor 2129 to be transmitted to therear wheel end, by regulating pressing forces of the main clutch 79 toadjust connection forces of the on-off clutch 5.

[0175] Further, the use of the on-off clutch 5 as a frictional clutcheliminates generation of ratchet sounds such as in meshing clutch forexample, and high of calmness.

[0176] The use of a frictional on-off clutch 5 eliminates shocks andshock sounds in clutch connection and cancellation thereof.

[0177] The frictional on-off clutch 5 does not need synchronization ofrotation in clutch connection and cancellation thereof, and nosynchronizing mechanism is necessary, so that the power transmissionsystem 1 can be the more light-weighted, compact, and reduced infabrication cost.

[0178] Further, because the main clutch 79, oil and the like are warmedby heat of the magnet 91 (coil 107), when connection of the on-offclutch 5 is cancelled, dragging torque to be produced at the rear wheelend by viscosity of oil, in particular when the oil temperature is low,can be reduced, allowing for the engine to have a commensurate reductionin loss of drive power, resulting in improved fuel consumption.

[0179] Because of unnecessary countermeasures such as lowering oilviscosity, raising temperature, and reducing amount of oil for thedragging torque to be reduced, implementation can be the more reduced incost.

[0180] Moreover, the electric motor 2129 is not mechanically rotated bydragging torque, protection performances such as of a battery,alternator, and circuit elements can be improved, as well as durabilityof the electric motor 2129.

[0181] The on-off clutch 5 is allowed to have an increased frictionalsurface area by use of the multi-plate main clutch 79, in addition tothat pressing forces of the main clutch 79 can be magnified by the ballcam 83. The clutch 5 can thus provide a sufficient capacity even whensmall-sized.

[0182] Therefore, the power transmission system 1 is allowed to handlegreat drive power, while the on-off clutch 5 to be compact in size canbe more light-weighted and compact, with improved vehicle-mountability.

[0183] Still more, because the on-off clutch 5 is variable in diamterand number of clutch plates of the main clutch 79, its capacity can bearibtrarily controlled, with an enhanced design flexibility.

[0184] In this embodiment in which the on-off clutch 5 is arranged tothe third shaft that is nearest to the differential apparatus 7 amongshafts of the speed-reducing mechanism 3, the on-off clutch 5 can bedisposed within a projection region of a large component, such as thering gear 31 of the differential apparatus 7, permitting the system 1 tobe entirely small-sized.

[0185] There will be described below various power transmission systemsaccording to other embodiments of the invention. It is noted that eachpower transmission system to be described is arranged on a rear wheelside of a four-wheel driven vehicle using both an engine as a main drivepower source and an electric motor 2129 as an auxiliary drive powersource, like the power transmission system 1 according to the firstembodiment, whereas front wheels of the vehicle are normally driven fromthe engine and rear wheels thereof are driven from the electric motor2129, when necessary.

Second Embodiment

[0186] With reference to FIG. 3, description is made of a transmissionsystem 201 of drive power of an electric motor 2129 according to thesecond embodiment of the invention and a method of operation thereof.

[0187] The power transmission system 201 has features of the 1^(st),2^(nd), 8^(th), 9^(th), 10^(th), and 12^(th) aspects of the invention.Note the terms “left” and “right” mean those of a vehicle equipped withthe power transmission system 201, and those in FIG. 3.

[0188] Like reference numerals are given to members having likefunctions as those of the power transmission system 1 according to the1^(st) embodiment of the invention. Those members with like functionsare not described to avoid redundancy.

[0189] The power transmission system 201 is constituted with aspeed-reducing mechanism 203, an on-off clutch 205 (as a clutch) to beelectromagnetically controlled, a rear differential 207 (as adifferential apparatus), a controller 2133, etc.

[0190] The power transmission system 201 is accommodated in a casing 9,which is constituted as a combination of a gear casing part 11 foraccommodating the speed-reducing mechanism 203 and a differentialcarrier part 13 for accommodating the rear differential 207 in which theon-off clutch 205 is incorporated.

[0191] The speed-reducing mechanism 203 is constituted with reductiongears equivalent to the reduction gear sets 15, 17, and 19 of the powertransmission system 1, and transmits drive torque of the electric motor2129 to the rear differential 207 in a speed-reducing manner.

[0192] A reduction gear 27 of the reduction gear set 17 is welded to athird axis 213, which is supported by ball bearings 215 and 217 fixed tothe gear casing part 11.

[0193] A reduction gear 29 of the reduction gear set 19 is formed on thethird shaft 213.

[0194] The rear differential 207 is provided with a differential case223, a rotary case 225, and a differential mechanism 227 of a bevel geartype.

[0195] The differential case 41 is constituted with a cover 229, aninput member 231, and an outer case 233 fastened by bolts 235 forfixation, and a reduction gear 31 of the reduction gear set 19 is formedon the input member 231.

[0196] The rotary case 225 is arranged so as to rotate relative to aninner periphery of the differential case 223.

[0197] The differential mechanism 227 is constituted with a plurality ofpinion shafts 237, pinion gears 239 individually supported by the pinionshafts 237, and output end side gears 241 and 243 meshing with thepinion gears 239.

[0198] The side gears 241 and 243 are splined on left and right rearaxles 67 and 69, respectively.

[0199] The on-off clutch 205 is configured for interconnection anddisconnection between the differential case 223 and the rotary case 225,as will be described.

[0200] When the on-off clutch 205 is engaged for interconnection, if theelectric motor 2129 is rotated, the differential case 223 is driven torotate, and this drive power is transmitted via the rotary case 225 andthe on-off clutch 205 to the pinion shafts 237, and is distributedtherefrom via the pinion gears 239, the side gears 241 and 243, and therear axles 67 and 69 to left and right rear wheels, rendering thevehicle four-wheel driven, with enhanced abilities such as for bad-roadescape and travel, start, acceleration, and vehicle body stabilization.

[0201] If a difference develop between rear wheel drive resistances suchas on a bad road, the pinion gears 239 individually revolve to effect adifferential distribution of the drive power from the electric motor2129 to the left and right rear wheels.

[0202] When rotation of the electric motor 2129 is stopped, the vehicleenters a two-wheel driven state with front wheels driven from theengine, where the controller 2133 cancels engagement of the on-offclutch 205, thereby interrupting the interconnection between theelectric motor 2129 and the rear wheels.

[0203] The on-off clutch 205 is constituted with a cone clutch 245 (as africtional clutch), a multi-plate pilot clutch 81, a ball cam 83, a camring 85, a pressure plate 87, a clutch ring 247, an armature 89, anelectric magnet 91, a controller 2133, etc.

[0204] The cone clutch 245 is constituted with an input member 231 onthe differential case 223 side, and cone parts 249, 249 formed betweenthe clutch ring 247 and the rotary case 225 on the differentialmechanism 227 side. The input member 231, the clutch ring 247, and therotary case 225 are made of a sintered metallic material, with asufficient resistance to abrasion.

[0205] The pilot clutch 81 is arranged between the cam ring 85 and arotor 95 on the outer case 233 (differential case 233) side.

[0206] The pressure plate 87 is movably connected to the right side gear243 by a spline part 251 provided therebetween, and the clutch ring 247is movably connected to the outer case 233 by a spline part 253.

[0207] The pressure plate 87 may not be connected to the side gear 243,but movably to the rotary case 225 side.

[0208] The controller 2133 is adapted, like the first embodiment, forexcitation of the magnet 91, control of exciting current, cease ofexcitation, etc., as well as for concurrent services to operate theelectric motor 2129 and the magnet 91 and stop the operations.

[0209] When the electric motor 2129 is rotated and the magnet 91 isexcited, the armature 89 presses the pilot clutch 81 to engage, so thatdifferential torque of the differential mechanism 227 (drive power fromthe electric motor 2129) is applied to the ball cam, via the cam ring 85connected by the pilot clutch 81 to the differential case 223 and thepressure plate 87 on he side gear 243 side. There is generated a camthrust force, which is received by the pressure plate 87, which is thusforced to move leftward, pressing the cone parts 249 via the clutch ring247, causing the cone clutch 245 to be engaged.

[0210] When the cone clutch 245 is thus engaged, drive power of theelectric motor 2129 is transmitted through respective reduction gearsets to the rear differential 207, rendering the vehicle four-wheeldriven.

[0211] As the exciting current of the magnet 91 is controlled, the pilotclutch 81 has a commensurate slip, changing the cam thrust force of theball cam 83, causing the cone clutch 245 to have a varied connectionforce, thereby controlling drive power to be transmitted from theelectric motor 2129 to the rear wheel end.

[0212] Such control of drive power can be effected while the vehicle isturning, with enhanced turnability and increased stability of thevehicle body.

[0213] When the excitation of the magnet 91 is stopped, the pilot clutch81 is released, causing the ball cam 83 to lose cam thrust force, andconnection of the cone clutch 245 is canceled, rendering the vehicletwo-wheel driven.

[0214] Like the first embodiment, the controller 2133 is adapted, whenthe vehicle starts, to rotate the electric motor 2129 and concurrentlyoperate the on-off clutch 205, so that the vehicle has increased drivepower, and respond to a critical vehicle speed by stopping rotation ofthe electric motor 2129, thereby canceling connection of the on-offclutch 205.

[0215] Further, when four-wheel driven to go up a slope, if the vehiclesuffers a rollback with front wheels idling, the controller 2133 isstops rotation of the electric motor 2129, canceling connection of theon-off clutch 205.

[0216] Like this, when connection of the on-off clutch 205 is canceled,the electric motor 2129 is cut off from the rear wheels, to be free fromforced rotation due to rotation of the rear wheels.

[0217] When increased drive torque is desirable to have an increasedability to run over a difference in level or cavity in a road, withstill enhanced accelerating ability, the controller 2133 may becontrolled to rotate the electric motor 2129 and connect the on-offclutch 205, thereby rendering the vehicle four-wheel driven.

[0218] The differential case 223 is formed with openings 255 and 257,and spiral oil grooves 263 and 265 in inner peripheries of boss parts259 and 261.

[0219] As the differential case 223 rotates, oil flows between thedifferential case 223 and an oil sump of the casing 9 via the openings255 and 257 and oil grooves 263 and 265. Oil flowing into thedifferential case 223 is sufficient for lubrication and cooling such asof meshing gear parts of the differential mechanism 227, cone clutch245, pilot clutch 81, ball cam 83, and bearings 99.

[0220] Heat of the coil 107 of the magnet 91 is used to warm oil in theoil sump, as well as the pilot clutch 81 and the ball cam 83therearound, and warmed oil warms the cone clutch 245.

[0221] The power transmission system 201 of the electric motor 2129 isthus constructed.

[0222] In the power transmission system 201, such as when the vehicle istwo-wheel driven or suffering a rollback, the electric motor 2129 isdisconnected from the rear wheels by the on-off clutch 205, asnecessary, and is released not to be forced to rotate by rotation of therear wheels.

[0223] In this power transmission system 201, the on-off clutch 205 isintegrated with the rear differential 207 and a frictional clutch (thecone clutch 245) is employed for the on-off clutch 205, whereby thereare achieved like effects to the power transmission system 1 of thefirst embodiment in which the on-off clutch 5 is integrated with aspeed-reducing mechanism and a frictional clutch (the multi-plate mainclutch 79) is employed for the on-off clutch 5.

[0224] The power transmission system- 201 has like effects to the firstembodiment, except those derived from disposing the on-off clutch 5between gears of the speed-reducing mechanism, using a multi-plateclutch for the on-off clutch 5, and using the gear pump 93 forlubrication.

[0225] In addition, as the cone clutch 245 is simple in structure andsmall in number of components, the power transmission system 201 can bethe more light-weighted, compact, and enhanced in vehicle-mountability,with low costs.

Third Embodiment

[0226] With reference to FIGS. 4 and 5, description is made of atransmission system 301 of drive power of an electric motor 2129according to the third embodiment of the invention and a method ofoperation thereof.

[0227] The power transmission system 301 has features of the 1^(st),2^(nd), 8^(th), 9^(th), 13^(th), and 14^(th) aspects of the inventionand the operating method has features of the 18 ^(th) and 19^(th)aspects of the invention. Note the terms “left” and “right” mean thoseof a vehicle equipped with the power transmission system 301, and thosein FIGS. 4 and 5. Like reference numerals are given to members havinglike functions as those of the power transmission systems 1 and 201according to the 1^(st) and 2^(nd) embodiments of the invention. Thosemembers with like functions are not described to avoid redundancy.

[0228] The power transmission system 301 is constituted with aspeed-reducing mechanism 303, a rear differential 305 (as a differentialapparatus), an on-off clutch 307 (as a clutch), a controller 2133, etc.

[0229] The speed-reducing mechanism 303 is analogous in structure to thespeed-reducing mechanism 3 or 203.

[0230] The rear differential 305 is provided with a differential case223, a rotary case 309, and a differential mechanism 227 of a bevel geartype.

[0231] Pinion shafts of the differential mechanism 227 are engaged withthe rotary case 309, and fixed by spring pins 311.

[0232] The on-off clutch 307 is constituted with a dog clutch 313 (as ameshing clutch), an operation mechanism 315 therefor, the controller2133, etc.

[0233] The dog clutch 313 is constituted with meshing teeth 319 and 321formed on a clutch ring 317 and the rotary case 309, respectively.

[0234] As shown in FIG. 4, the clutch ring 317 is constituted with abase part 323 formed with the meshing teeth 319, and a plurality of armparts 325 formed on the base part 323. The arm parts 325 projectoutward, engaging with an opening 327 of the differential case 223, foraxially movably connecting the differential case 223 to the clutch ring317.

[0235] When the clutch ring 317 moves rightward, the meshing teeth 319and 321 (as the dog clutch 313) mesh each other, and when the clutchring 317 returns leftward, the meshing of the dog clutch 313 iscanceled.

[0236] In a meshing state of the dog clutch 313, rotation of thedifferential case 223 is transmitted from the rotary case 390 to thedifferential mechanism 227. When the meshing of the dog clutch 313 iscanceled, the rotary case 309 and subsequent components on the rearwheel side are disconnected.

[0237] Further, as in FIG. 4, the meshing teeth 319 of the clutch ring317 has a cam angle α, and the meshing teeth 321 of the rotary case 309have the same cam angle.

[0238] In a meshing engagement of the dog clutch 313 with transmissiontorque applied on the meshing teeth 319 and 321, the above-noted camangle produces a cam thrust force 329 in a direction for the clutch ring317 to be moved toward a meshing canceling side.

[0239] The operation mechanism 315 is constituted with an operation ring331, a shift fork 333, a shift rod 335, a swing shaft 337, a motor 339controllable for switching the direction of rotation, a direction changegear mechanism 341, etc.

[0240] The operation ring 331 is fixed to the clutch ring 317, and theshift fork 333 is slidably engaged with a circumferential groove 343 ofthe operation ring 331. The shift fork 333 is fixed onto the shift rod335, and the shift rod 335 is movably engaged with support holes 345 and347 of the differential carrier part 13, for guiding the shift fork 333to axially move.

[0241] The swing shaft 337 is formed with a convex part 349, which isengaged with a concave part of the shift fork 333.

[0242] Drive power of the motor 339 is changed in direction by thedirection change gear mechanism 341, to swing the swing shaft 337. Whenthe swing shaft 337 is swung, the shift fork 333 is moved, acting viathe clutch ring 317 on the operation ring 331 to move, and when thedirection of rotation of the motor 339 is changed, the swing shaft 337is swung in a changed direction, whereby the clutch ring 317 isreciprocally operated.

[0243] The dog clutch 313 is thus operated for connection anddisconnection.

[0244] The controller 2133 is adapted, like the first or secondembodiment, to assist drive power of the engine by drive power of heelectric motor 2129 when the vehicle starts, and at a critical vehiclespeed, to stop rotation of the electric motor 2129, while controllingthe motor 339 to cancel meshing engagement of the dog clutch 313.

[0245] Further, when four-wheel driven to go up a slope, if the vehiclesuffers a rollback, the controller 2133 stops rotation of the electricmotor 2129, canceling meshing of the dog clutch 313.

[0246] Like this, when meshing of the dog clutch 313 is canceled, theelectric motor 2129 is cut off from the rear wheels, to be free fromforced rotation due to rotation of the rear wheels.

[0247] When increased drive torque is desirable in travel to have anincreased ability to run over a difference in level or cavity in a road,with still enhanced accelerating ability, the controller 2133 may becontrolled to rotate the electric motor 2129 and bring the dog clutch313 into meshing, thereby rendering the vehicle four-wheel driven.

[0248] Like this, the cancellation of meshing of the dog clutch 313 ispromoted when the clutch ring 317 is pressed in the meshing cancelingdirection with the cam thrust force 329 developed at the meshing teeth319 and 321.

[0249] When canceling meshing of the dog clutch 313, the controller 2133follows an operation method according to the invention, in whichrevolution number of the driving electric motor 2129 is changed tothereby give the meshing teeth 319 and 321 adequate vibrations to reducefrictional resistance, or rotational direction of the driving electricmotor 2129 is switched to thereby give the meshing teeth 319 and 321adequate vibrations to reduce frictional resistance.

[0250] By the cam thrust force 329 and vibrations to the meshing teeth319 and 321, the cancellation of meshing of the dog clutch 313 can beperformed in a fast response.

[0251] Further, oil flows from an oil sump of the casing 9 via theopenings 255 and 257 and oil grooves of boss parts 259 and 261 into thedifferential case 223, giving sufficient lubrication and cooling to gearmeshing parts of the differential mechanism 227, the dog clutch 313,etc.

[0252] Heat of the coil 107 of the magnet 91 is used to warm oil in theoil sump, as well as the pilot clutch 81 and the ball cam 83therearound, and warmed oil warms the cone clutch 245.

[0253] The power transmission system 301 of the electric motor 2129 isthus constructed.

[0254] In the power transmission system 301, such as when the vehicle istwo-wheel driven or suffering a rollback, the electric motor 2129 isdisconnected from the rear wheels by the on-off clutch 307, and isreleased not to be forced to rotate by rotation of the rear wheels.

[0255] In this power transmission system 301, the dog clutch 313 isintegrated with the rear differential 305 and a frictional clutch (thedog clutch 313) is employed for the on-off clutch 307, whereby there areachieved like effects to the power transmission system 1 of the firstembodiment in which the on-off clutch 5 is integrated with aspeed-reducing mechanism and a frictional clutch (the multi-plate mainclutch 79) is employed for the on-off clutch 5.

[0256] The power transmission system 301 has like effects to the firstembodiment, except those derived from disposing the on-off clutch 5between gears of the speedreducing mechanism, using a multi-plate clutchfor the on-off clutch 5, and using the gear pump 93 for lubrication.

[0257] In addition, as the dog clutch 313 is small in size and large incapacity, the power transmission system 301 is allowed to handle greatdrive power and to be the more light-weighted, compact, and enhanced invehicle-mountability.

[0258] The dog clutch 313 is simple in structure and small in componentnumber, so that the power transmission system 301 can be fabricated withthe lower cost.

[0259] In addition, because the dog clutch 313 (as a meshing clutch) isfree from dragging torque due such as to viscosity of oil, unlike thefrictional clutches, the loss of drive power is little, allowingenhanced fuel consumption.

[0260] Because of unnecessary countermeasures such as lowering oilviscosity, raising temperature, and reducing amount of oil for thedragging torque to be reduced, implementation can be the more reduced incost.

[0261] Moreover, because the electric motor 2129 is not mechanicallyrotated by dragging torque, protection performances such as of abattery, alternator, and circuit elements can be improved, as well asdurability of the electric motor 2129.

[0262] Further, when canceling connection of the on-off clutch 307, thecancellation of meshing of the dog clutch 313 is promoted by the motor,so that connection of the on-off clutch 307 can be canceled at anintended instance or a critical vehicle speed, and the vehicle can bechanged over from a four-wheel driven state to a two-wheel driven statein a necessary timing.

[0263] Therefore, the power transmission system 301 is allowed to havehigh protection performances such as of the electric motor 2129,battery, alternator, circiut elements, etc.

Fourth Embodiment

[0264] With reference to FIGS. 6 to 8, description is made of atransmission system 401 of drive power of an electric motor 2129according to the fourth embodiment of the invention and a method ofoperation thereof.

[0265] The power transmission system 401 has features of the 1^(st),2^(nd), 8^(th), 9^(th), 13^(th), and 14^(th) aspects of the invention,and the operating method has features of the 18^(th) and 19^(th) aspectsof the invention. Note the terms “left” and “right” mean those of avehicle equipped with the power transmission system 401, and those inFIGS. 6 to 8. Like reference numerals are given to members having likefunctions as those of the power transmission systems 1, 201 and 301according to the 1^(st), 2^(nd) and 3^(rd) embodiments of the invention,respectively. Those members with like functions are not described toavoid redundancy.

[0266] The power transmission system 401 is constituted with aspeed-reducing mechanism 403, a rear differential 405 (as a differentialapparatus), an on-off clutch 407 (as a clutch), a controller 2133, etc.

[0267] The speed-reducing mechanism 403 is analogous in structure to thespeed-reducing mechanism 3, 203, or 303.

[0268] The rear differential 405 is provided with a differential case223, a rotary case 409, and a differential mechanism 227 of a bevel geartype.

[0269] Pinion shafts 237 of the differential mechanism 227 are engagedwith the rotary case 309, to be fixed.

[0270] The on-off clutch 407 is constituted with a dog clutch 411 (as ameshing clutch), an electric magnet 413, the controller 2133, etc.

[0271] As shown in FIG. 7 and FIG. 8, the dog clutch 411 is constitutedwith meshing teeth 417 and 419 formed on the differential case 223 andan armature 415, respectively.

[0272] The armature 415 is axially movably connected to the rotary case409 by a meshing part 421 formed therebetween.

[0273] As shown in FIG. 7, when the armature 415 moves leftward, themeshing teeth 417 and 419 (as the dog clutch 411) mesh each other, andas shown in FIG. 8, when the armature 415 returns rightward, the meshingof the dog clutch 411 is canceled.

[0274] In a meshing state of the dog clutch 411, rotation of thedifferential case 223 is transmitted from the rotary case 409 to thedifferential mechanism 227. When the meshing of the dog clutch 411 iscanceled, the rotary case 409 and subsequent components on the rearwheel side are disconnected.

[0275] Further, as in FIG. 8, the meshing teeth 417 and 419 of the dogclutch 411 have a cam angle α, and the meshing part 421 has a smallercam angle γ.

[0276] When transmission torque is applied on the meshing part 421, thesmaller cam angle γ produces a cam thrust force in a direction for thearmature 415 to be moved toward a meshing side of the dog clutch 411. Ina meshing engagement with transmission torque applied on the meshingteeth 417 and 419, the cam angle β produces a cam thrust force in adirection for the armature 415 to be moved toward a meshing cancelingside of the dog clutch 411. As a result, the armature 415 is pressed inthe meshing canceling side (FIG. 8) by a differential cam thrust force423 (FIG. 7).

[0277] The magnet 413 has a core 425 connected to an inside of thedifferential carrier part 13 by a connection member 427 and a bolt 429,and lead wires drawn out therefrom through the differential carrier part13, to be externally connected to a vehicle-mounted battery.

[0278] When the magnet 413 is excited, the armature 415 is attractedleftward, causing the dog clutch 411 to mesh. When the excitation of themagnet 413 is stopped, as in FIG. 7, the meshing engagement of the dogclutch 411 is canceled by the cam thrust force 423.

[0279] The controller 2133 is adapted, like the first, second, or thirdembodiment, when increased vehicle drive torque is desirable, to rotatethe electric motor 2129, thereby causing the dog clutch 411 to mesh,rendering the vehicle four-wheel driven.

[0280] Further, when the vehicle is in a two-wheel driven state or whensuffering a rollback, the controller 2133 stops rotation of the electricmotor 2129, canceling meshing of the dog clutch 411, so that theelectric motor 2129 is disconnected from rear wheels, to be free fromforced rotation due to rotation of the rear wheels.

[0281] Like this, the cancellation of meshing of the dog clutch 411 ispromoted by the cam thrust force 423.

[0282] When canceling meshing of the dog clutch 411, the controller 2133follows an operation method according to the invention, in whichrevolution number of the driving electric motor 2129 is changed, orrotational direction thereof is switched to thereby give the meshingteeth 417 and 419 adequate vibrations to reduce frictional resistance.

[0283] By the cam thrust force 423 and vibrations to the meshing teeth417 and 419, the cancellation of meshing of the dog clutch 411 can beperformed in a fast response.

[0284] Further, oil flows from an oil sump of the casing 9 via openingsand oil grooves of boss parts 259 and 261 into the differential case223, giving sufficient lubrication and cooling to gear meshing parts ofthe differential mechanism 227, the dog clutch 411, etc.

[0285] Heat of a coil 431 of the magnet 413 is used to warm oil in theoil sump, and warmed oil flows into the differential case 223, warms thedog clutch 411, as well as the meshing part 421, to promote movement ofthe armature 415, thereby smoothing meshing cancellation of the dogclutch 411.

[0286] The power transmission system 401 of the electric motor 2129 isthus constructed.

[0287] In the power transmission system 401, such as when the vehicle istwo-wheel driven or suffering a rollback, the electric motor 2129 isdisconnected from the rear wheels by the on-off clutch 407 (dog clutch411), and is released not to be forced to rotate by rotation of the rearwheels.

[0288] In this power transmission system 401, the on-off clutch 407 isconstituted with the dog clutch 411 (a frictional clutch), the powertransmission system 401 is allowed to have like effects to powertransmission system 301 according to the third embodiment that alsoemploys a frictional clutch.

Fifth Embodiment

[0289] With reference to FIGS. 9 to 11, description is made of atransmission system 501 of drive power of an electric motor 2129according to the fifth embodiment of the invention and a method ofoperation thereof.

[0290] The power transmission system 501 has features of the 1^(st),2^(nd), 6^(th), 7^(th), 8^(th), 9^(th), 13^(th), and 14^(th) aspects ofthe invention and the operating method has features of the 18^(th) and19^(th) aspects of the invention. Note the terms “left” and “right” meanthose of a vehicle equipped with the power transmission system 501, andthose in FIGS. 9 to 11. Like reference numerals are given to membershaving like functions as those of the power transmission systems 1, 201,301 and 401 according to the 1^(st), 2^(nd), 3^(rd) and 4^(th)embodiments of the invention. Those members with like functions are notdescribed to avoid redundancy.

[0291] The power transmission system 501 is constituted with aspeed-reducing mechanism 3, an on-off clutch 503 (as a clutch), a reardifferential 7, a controller 2133, etc.

[0292] The on-off clutch 503 is interposed between an outer shaft 37 andan inner shaft 39 of the speed-reducing mechanism 3, and controlled bythe controller 2133 in synchronism with a rear wheel driving electricmotor 2129.

[0293] The on-off clutch 503 is constituted with a dog clutch 505 (as ameshing clutch), a sync hub 507, a coupling sleeve 509, a synchronizedgear 511, a synchronizer 513, a ball cam 515, needle bearings 517, anoperation wire 519, a direction change means 521, etc.

[0294] As shown in FIG. 10 and FIG. 11, the dog clutch 505 isconstituted with meshing teeth 523 formed on a right part of thecoupling sleeve 509, and meshing teeth 525 on the synchronized gear 511.

[0295] The sync hub 507 is spline connected on an outer periphery of theinner shaft 39. The coupling sleeve 509 is axially movably connected viaa key to an outer peripheral side of he sync hub 507.

[0296] The synchronized gear 511 is integrally formed on a left end ofthe outer shaft 37.

[0297] The synchronizer 513 is configured to synchronize rotationsbetween the coupling sleeve 509 (the inner shaft 39) and thesynchronized gear 511 (the outer shaft 37), for a match in phase betweenthe meshing teeth 523 and 525.

[0298] The ball cam 515 is constituted, as shown in FIG. 10 and FIG. 11,balls 533 arranged between a cam groove 527 formed in a gear casing part11 and a cam groove 531 formed in the cam ring 529.

[0299] The needle bearings 517 are interposed between the cam ring 529and the coupling sleeve 509, for isolating rotation of he couplingsleeve 509 (outer shaft 37 and inner shaft 39) from the cam ring 529 toprevent erroneous actions of the ball cam 515.

[0300] The operation wire 519 is reciprocally operated by an actuator ofwhich actions are controlled by the controller 2133.

[0301] The actuator of the operation wire 519, as well as an actuatorfor operating the coupling sleeve 509 to move, may preferably be amelectromagnetic actuator, a fluid actuator such as a pneumatic orhydraulic actuator, or an actuator using an electric motor.

[0302] The direction change means 521 is configured for changing areciprocal movement of the operation wire 519 into a rotationaldirection or angular movement to thereby rotate the cam ring 529 of theball cam 515.

[0303] As shown in FIG. 10, by the cam ring 529 rotated in an arrowdirection 535, the ball cam 515 is operated to produce a cam thrustforce 537.

[0304] The meshing teeth 523 and 525 of the dog clutch 505 have a camangle δ. In a meshing engagement of the dog clutch 505 with transmissiontorque applied to the meshing teeth 523 and 525, the above-noted camangle produces a cam thrust force 539 in a direction for the couplingsleeve 590 to be moved toward a meshing canceling side.

[0305] The cam thrust force 537 of the ball cam 515, which is greaterthan the above-noted cam thrust force 539, acts via the needle bearings517 on the coupling sleeve 509 to move rightward. As the coupling sleeve509 moves rightward, the synchronizer 513 operates for synchronizationbetween the coupling sleeve 509 and the synchronized gear 511 to rotate,and when they are synchronized, the meshing teeth 523 of the couplingsleeve 509 and the meshing teeth 525 of the synchronized gear 523 mesheach other, so that the dog clutch 505 is brought into meshingengagement.

[0306] When the operation wire 519 is operated in an opposite direction,the direction change means 521 rotates the cam ring 529 in a reversedirection to arrow 535. Along therewith, the cam thrust force 537 of theball cam 515 disappers, so that as shown in FIG. 11 the coupling sleeve509 returns leftward, canceling the meshing engagement of the dog clutch505.

[0307] While the dog clutch 505 is meshing, drive powre of the electricmotor 2129 is transmitted through reduction gear sets 15, 17, and 19 tothe rear differential 7, rendering the vehicle four-wheel driven.

[0308] When the meshing engagement of the dog clutch 505 is canceled,the electric motor 2129 is disconnected from the reduction gear set 19and subsequent components on the rear wheel side.

[0309] The controller 2133 is adapted, like the first, second, third, orfourth embodiment, for operating the electric motor 2129 to make the dogclutch 505 meshing, rendering the vehicle four-wheel driven, whengreater drive torque is desirable.

[0310] Further, when the vehicle is two-wheel driven or suffering arollback, the controller 2133 stops rotation of the electric motor 2129,canceling meshing of the dog clutch 505, so that the electric motor 2129is set free from being forced to rotate by rotation of the rear wheels.

[0311] Like this, the cancellation of meshing of the dog clutch 505 ispromoted by the cam thrust force 539 of the meshing teeth 523 and 525.

[0312] When canceling meshing of the dog clutch 505, the controller 2133follows an operation method according to the invention, in whichrevolution number of the driving electric motor 2129 is, or rotationaldirection of the driving electric motor 2129 is switched, to therebygive the meshing teeth 523 and 525 adequate vibrations to reducefrictional resistance.

[0313] By the cam thrust force 529 and vibrations to the meshing teeth523 and 525, the cancellation of meshing of the dog clutch 313 can beperformed in a fast response.

[0314] The dog clutch 505, sync hub 507, coupling sleeve 509,synchronized gear 511, synchronizer 513, ball cam 515, needle bearings517, operation wire 519, direction change means 521, and the likeconstituting the on-off clutch 503 are exposed inside the casing 9, andimmersed at lower parts in an oil sump. Further, oil is splashed aboutby rotation of the sync hub 507, coupling sleeve 509, synchronized gear511, etc.

[0315] Therefore, the dog clutch 505 (meshing teeth 523 and 525),synchronizer 513, ball cam 515 (cam grooves 527 and 531, and balls 533),needle bearings 517, direction change means 521, and the like are welllubricated and cooled.

[0316] The power transmission system 501 of the electric motor 2129 isthus constructed.

[0317] In the power transmission system 501, such as when the vehicle istwo-wheel driven or suffering a rollback, the electric motor 2129 isdisconnected from the rear wheels by the on-off clutch 503, and isreleased not to be forced to rotate by rotation of the rear wheels.

[0318] In this power transmission system 501, the dog clutch 505 isemployed for the on-off clutch 503, whereby there are achieved likeeffects to the power transmission system 301 or 401 of the third orfourth embodiment in which a meshing clutch is employed.

[0319] In this embodiment, the on-off clutch S is provided on a thirdshaft that is nearest to the differential apparatus 7 among shafts ofthe speed-reducing mechanism 3. Therefore, the system can be entirelycompact in size, by disposing the on-off clutch 5 within a projectionregion of a large component such as a ring gear 31 of the differentialapparatus 7.

Sixth Embodiment

[0320] With reference to FIG. 12, description is made of a transmissionsystem 601 of drive power of an electric motor 2129 according to thesixth embodiment of the invention and a method of operation thereof.

[0321] The power transmission system 601 has features of the 1^(st),2^(nd), 6^(th), 7^(th), 8^(th), 9^(th) and 13^(th) aspects of theinvention, and the operating method has features of the 18^(th) and19^(th) aspects of the invention. Note the terms “left” and “right” meanthose of a vehicle equipped with the power transmission system 601, andthose in FIG. 12. Like reference numerals are given to members havinglike functions as those of the power transmission systems 1, 201, 301,401 and 501 according to the 1^(st), 2^(nd), 3^(rd), 4^(th) and 5^(th)embodiments of the invention, respectively. Those members with likefunctions are not described to avoid redundancy.

[0322] The power transmission system 601 is constituted with aspeed-reducing mechanism 3, a rear differential 7 (as a differentialapparatus), an on-off clutch 603 (as a clutch), a controller 2133, etc.

[0323] The on-off clutch 603 is arranged between outer and inner shafts37 and 39, being responsible for command of the controller 2133 to beengaged and disengaged, in interconnection with electrical motor 2129,as described below.

[0324] The on-off clutch 603 is constituted with a meshing clutch 605, async hub 607, a coupling sleeve 609, a synchronization gear 611, asynchronizer 613, a shift fork 625, an operation rod 627 and an air-typeactuator 629.

[0325] The meshing clutch 605 is constituted with a meshing tooth 631that is formed to the coupling sleeve 609 on its inner periphery, and ameshing tooth 633 that is formed to the synchronization gear 611 on itsouter periphery.

[0326] The sync hub 607 is spline connected to an outer periphery of theinner shaft 39. The coupling sleeve 609 is connected to an outerperiphery of sync hub 607 through a key for axial movement.

[0327] The gear 611 is formed integrally to the outer shaft 37 at itsleft end.

[0328] The synchronizer 613 synchronizes rotations with coupling sleeve609 (inner shaft) and synchronization gear 611 (outer shaft) to setphases of meshing tooth 631 and 633.

[0329] The shift fork 625 is slidably engaged with a circular groove 635defined by coupling sleeve 609, being fixed on the operation rod 627.

[0330] The operation rod 627 is movably engaged with a supporting holeof the gear casing 11 to guide axial movement of shift fork 625. Theoperation rod 627 and gear casing 11 have an oil seal 637 arrangedtherebetween, the oil seal being for an oil to be prevented from leak tothe outside.

[0331] The actuator 629 is linked to operation rod 627. Its pressurechamber 639 is connected to a pressure source that includes an air pumpand accumulator through a valve mechanism.

[0332] The controller 2133 operates the valve mechanism to feed an airat a pressure to pressure chamber 639, thus to work actuator 629, or tolet an air out to stop actuator 629.

[0333] The operation of actuator 629 moves shift fork 625 throughoperation rod 627 rightward to move coupling sleeve 609 rightward.

[0334] The rightward movement of coupling sleeve 609 operatessynchronizer 613. When the coupling sleeve 609 and synchronization gear611 synchronizes in rotation, the meshing teeth 631 and 633 of couplingsleeve 509 and synchronization gear 611, as shown by doubled-dots brokenline, are meshed with each other, thus to engage the meshing clutch 605.

[0335] When the operation of actuator 629 is stopped, coupling sleeve609 is brought back leftward, which disengages the meshing of clutch605.

[0336] When meshing clutch 605 is in engagement, a drive force of theelectric motor 2129 is transmitted through the reduction gear sets 15,17 and 19 to the rear deferential 7, which renders the vehicle infour-wheel driven state. When the meshing clutch 605 is indisengagement, the electric motor 2129 detached from reduction gear set19 at rear wheels.

[0337] The controller 2133, as similar to the first, second, third,fourth and fifth embodiments, operates electric motor 2129 for increaseof drive torque of a vehicle, to engage the dog clutch 605 forfour-wheel driven state.

[0338] When occurring two-wheel driven state or rollback state, theelectric motor 2129 is stopped in rotation for the dog clutch 605 to bedisengaged for detachment of the motor 2129 from the rear wheels, whichallows front wheels to be prevented from forced rotation by rotation ofrear wheels.

[0339] When the clutch 605 is disengaged, feed of an air of negativepressure to actuator 629 accelerates the disengagement of meshing.

[0340] In addition, when the controller 2133 disengages the meshingclutch 605, the number of rotation of electric motor 2129 in accordancewith the operation method of embodiment, or switch of rotationaldirection gives the meshing teeth 631 and 633 appropriate vibrations forreduction of friction resistance.

[0341] The air of negative pressure and vibrations to be give to meshingteeth 631 and 633 allows the disengagement of meshing clutch 605 to beperformed at remarkably quick response.

[0342] The meshing clutch 605, constituting the on-off clutch 603, isexposed inside the casing 9, a lower half portion of which is immersedin an oil sump and to the periphery of which rotations of the sync hub607, coupling case 609 and synchronization gear 611 splash oil.

[0343] Thus, the meshing clutch 605 (meshing teeth 631 and 633) andsynchronizer 613 is lubricated and cooled sufficiently.

[0344] This constitutes the electric motor 2129 and transmission system601 of drive power.

[0345] The transmission system 601 detaches the electric motor 2129 andrear wheels from each other by the on-off clutch 603 (meshing clutch605) in a two-wheel driven state or rollback, and the electric motor isnot forced to rotate by rotation of the rear wheels.

[0346] In addition, the transmission system 601 employs the meshingclutch 605 for on-off clutch 603, to obtain benefits equivalent to thoseof the transmission systems 301, 401 and 501 of the third, fourth andfifth embodiments employing the meshing clutches.

[0347] The embodiment has the on-off clutch 5 that is provided to thethird shaft closest to the differential 7 in the speed-reducingmechanism 3, and within projection region of a large component, such asthe ring gear 31 of differential 7, is arranged the on-off clutch 5,which allows the differential to be entirely small in size.

[0348] The actuator 629 may be hydraulically operated.

Seventh Embodiment

[0349] With reference to FIG. 13, description is made of a transmissionsystem 701 of drive power of an electric motor 2129 according to thefifth embodiment of the invention and a method of operation thereof.

[0350] The power transmission system 701 has features of the 1^(st),2^(nd), 6^(th), 7^(th), 8^(th), 9^(th), 13^(th) and 14^(th) aspect s ofthe invention and the operating method has features of the 18^(th) and19^(th) aspects of the invention. Note the terms “left” and “right” meanthose of a vehicle equipped with the power transmission system 701, andthose in FIG. 13. Like reference numerals are given to members havinglike functions as those of the power transmission systems 1, 201, 301,401, 501 and 601 according to the 1^(st), 2^(nd), 3^(rd), 4^(th), 5^(th)and 6^(th) embodiments of the invention. Those members with likefunctions are not described to avoid redundancy.

[0351] The power transmission system 701 includes a speed-reducingmechanism 3, an on-off clutch 703 for electromagnetic control (as aclutch), a rear differential 7 and a controller 2133.

[0352] The on-off clutch 703 is disposed between an outer shaft 37 andan inner shaft 39 of the speed-reducing mechanism 3, and isconnected/disconnected in association with the electric motor 2129 fordriving rear wheels by the controller 2133.

[0353] The on-off clutch 703 has a dog clutch 705 (meshing clutch), anarmature 707, a clutch ring 709, a return spring 711, an electromagnet713 and other components.

[0354] The dog clutch 705 has a mating tooth 715 formed on a left partof the armature 707 and a mating tooth 717 formed on a right part of theclutch ring 709.

[0355] The armature 707 is connected to the outer shaft 37 movably inthe axial direction with a spline member 719 provided therebetween. Theclutch ring 709 is connected to the inner shaft 39 with a spline member721 provided therebetween to be positioned with the snap ring 723 in theaxial direction.

[0356] The return spring 711 is disposed between the armature 707 andthe clutch ring 709, and biases the armature 707 to the right (in thedirection that cancels engagement of the dog clutch 705).

[0357] A core 725 of the electromagnet 713 is fixed inside of a gearcasing 11 via a connecting member 727 and a bolt 729. Its lead wire 731is pulled out from the gear casing 11 to be connected to a batterymounted on the vehicle.

[0358] When the electromagnet 713 is excited, the armature 707 isattracted to the left to establish engagement of the dog clutch 705.When the excitation of the electromagnet 713 is stopped, the armature707 is returned to the right by a biasing force of the return spring 711to cancel the engagement of the dog clutch 705.

[0359] When the dog clutch 705 is engaged, drive power of the electricmotor 2129 is transmitted to the rear differential 7 through reductiongear sets 15, 17 and 19 to make the vehicle in a four-wheel drivenstate. When the engagement of the dog clutch 705 is cancelled, theelectric motor 2129 is disconnected form the reduction gear set 19 andthe subsequent components on the rear wheel side.

[0360] As in 1^(st), 2^(nd), 3^(rd), 4^(th), 5^(th) and 6^(th)embodiments, when it is desired to increase drive torque of the vehicle,the controller 2133 actuates the electric motor 2129 for driving rearwheels to make the dog clutch 705 in engagement to provide a four-wheeldrives state.

[0361] A two-wheel driven state or a rollback phenomenon is generated,rotation of the drive electric motor 2129 is stopped to cancel theengagement of the dog clutch 705 and disconnect the electric motor 2129from the rear wheels to prevent the motor 2129 from being forcefullyrotated with the rotation of the rear wheels.

[0362] As described above, the cancellation of engagement of the dogclutch 705 is accelerated by a biasing force of the return spring 711.

[0363] Further, when canceling engagement of the dog clutch 705, thecontroller 2133 changes the number of rotation of the drive electricmotor 2129 in accordance with the operation method of the embodiment orchanges the rotational direction to give appropriate vibration to themating teeth 715 and 717 to reduce their frictional resistance.

[0364] The biasing force of the return spring 711 and the vibrationgiven to the mating teeth 715 and 717 allows the cancellation ofengagement of the dog clutch 705 with significantly quick response.

[0365] Further, the dog clutch 705 constituting the on-off clutch 703,the electromagnet 713 or other components are exposed inside of thecasing 9, and the half-bottom parts thereof are immersed in an oil sumpand are splashed around with oil with rotation of the armature 707, theclutch ring 709 and other components.

[0366] Accordingly, the dog clutch 705 (mating teeth 715 and 717), thespline member 719 and other components are sufficientlylubricated/cooled to accelerate movement of the armature 707 tofacilitate cancellation of engagement of the dog clutch 705.

[0367] The electromagnet 713 is cooled with oil to have stabledproperties and also warms the oil, eliminating the need for measuressuch as reducing the viscosity of the oil or raising temperature.

[0368] The transmission system 701 of drive power of the electric motor2129 is constituted in this manner.

[0369] When in a two-wheel driven state or a rollback phenomenon isgenerated, the on-off clutch 703 (dog clutch 705) disconnects theelectric motor 2129 from the rear wheels, preventing the electric motor2129 from being forcefully rotated.

[0370] In addition, the power transmission system 701 employs the dogclutch (meshing clutch) for the on-off clutch 703, having similareffects to those of the power transmission systems 301, 401, 501 and 601of the 3^(rd), 4^(th), 5^(th) and 6^(th) embodiments in which a meshingclutch is used.

[0371] Further, in this embodiment, the on-off clutch 5 is provided at athird shaft closest to the differential system 7 in the speed-reducingmechanism 3, so that the on-off clutch 5 can be disposed within aprojection region of larger components such as the ring gear 31 of thedifferentia system 7, to make the entire system compact.

Eighth Embodiment

[0372] With reference to FIG. 14, description is made of a transmissionsystem 801 of drive power of an electric motor 2129 according to theeighth embodiment of the invention and a method of operation thereof.

[0373] The power transmission system 801 has features of the 1^(st),2^(nd), 8^(th), 9^(th) and 15^(th) aspects of the invention and theoperating method has features of the 18^(th) and 19^(th) aspects of theinvention. Note the terms “left” and “right” mean those of a vehicleequipped with the power transmission system 801, and those in FIG. 14.Like reference numerals are given to members having like functions asthose of the power transmission systems 1, 201, 301, 401, 501, 601 and701 according to the 1^(st), 2^(nd), 3^(rd), 4^(th), 5^(th), 6^(th) and7^(th) embodiments of the invention. Those members with like functionsare not described to avoid redundancy.

[0374] The power transmission system 801 includes a speed-reducingmechanism 3, a rear differential 803, a one-way clutch 805 (as aclutch), an on-off clutch 807, a controller 2133, etc.

[0375] The rear differential 803 has a differential case 223, a rotationcase 809, and a bevel gear-type differential mechanism 227.

[0376] A pinion shaft 237 of the differential mechanism 227 is engagedwith the rotation case 809 to be fixed.

[0377] The one-way clutch 805 is disposed between the rotation case 809and the differential case 223 in the direction that transmits drivepower of the electric motor 2129 to rear wheels when the vehicle runsforward (in the direction that establishes connection of the clutch 805in a torque direction where the differential case 223 rotates before therotation case 809).

[0378] Accordingly, when the electric motor 2129 is rotated, theresultant drive power reduced by reduction gear sets 15, 17 and 19 istransmitted from the one-way clutch 805 to the differential mechanism227 to be distributed to the right and left rear wheels, making thevehicle in a four-wheel driven state.

[0379] When rotation of the electric motor 2129 is stopped, the rotationcase 809 on the rear wheel side rotates before the differential case 223to cancel connection of the one-way clutch 805, making the vehicle in atwo-wheel driven state, and the rotation of the rear wheels is isolatedfrom the electric motor 2129, preventing the electric motor 2129 frombeing forcefully rotated by rotation of the rear wheels.

[0380] The on-off clutch 807 has a dog clutch 811 (meshing clutch), anair actuator 813 for operation thereof, a return spring 815 and acontroller 2133.

[0381] The dog clutch 811 has mating teeth 819 and 821 formed in aclutch ring 817 and the rotation case 809, respectively.

[0382] The clutch ring 817 has, like the dog clutch 313 (in the thirdembodiment), a proximal part with the engaging tooth 819 and a pluralityof arms formed at the proximal part. The arms are protruded to theoutside, engaging with an opening of the differential case 223 so as toconnect the clutch ring 817 movably in the axial direction to thedifferential case 223.

[0383] The clutch ring 817 moving to the right engages the mating teeth819 and 821 (dog clutch 811) with each other, and the clutch ring 817returning to the left cancels the engagement of the dog clutch 811.

[0384] Upon the engagement of the dog clutch, rotation of thedifferential case 223 is transmitted from the rotation case 809 to thedifferential mechanism 227. Upon the disengagement of the dog clutch811, the rotation case 809 and the subsequent components on the rearwheel side are disconnected.

[0385] Like the dog clutch 313, the mating teeth 819 and 821 of the dogclutch 811 each have a cam angle. When transmission torque is applied tothe mating teeth 819 and 821, the cam angle causes a cam thrust force ina direction that moves the clutch ring 817 to the engagement-cancelledside.

[0386] The return spring 815 biases the clutch ring 817 to theengagement-cancelled side at any time.

[0387] A pressure chamber 823 of an actuator 813 is connected to apressure source comprising an air pump and an accumulator via an airflowpath 825 and a valve device.

[0388] The controller 2133 operates the valve device to send airpressure to the pressure chamber 823 to activate the actuator 813, andrelease the pressure to stop the operation of the actuator 813.

[0389] The actuator 813, when activated, moves the clutch ring 817 tothe right to engage the mating teeth 819 and 821 (dog clutch 811) witheach other. When the actuator 813 is stopped, the cam thrust force dueto the cam angle and the biasing force of the return spring 815 returnsthe clutch ring 817 to the left to cancel the engagement of the dogclutch 811.

[0390] For example, when the vehicle runs backward, the connection ofthe on-off clutch 807 (dog clutch 811) transmits drive power of theelectric motor 2129 to the differential mechanism 227 to allow backwardrunning in a four-wheel driven state.

[0391] At the time of forward running, the connection of the on-offclutch 807 distributes drive power of the electric motor 2129 to boththe one-way clutch 805 and the dog clutch 811, so that load on theclutches is reduced, improving durability and making their capacitiessmaller.

[0392] The controller 2133, when the vehicle starts moving, for example,rotates the electric motor 2129 with the connection of the on-off clutch807 cancelled, to drive the rear wheels via the one-way clutch 805 andassist drive power of the engine, as well as to stop rotation of theelectric motor 2129 at a prescribed vehicle speed.

[0393] When rotation of the electric motor 2129 is stopped, connectionof the one-way clutch 805 is cancelled regardless of vehicle speed whilethe vehicle runs, to disconnect the electric motor 2129 from the rearwheels to prevent the motor 2129 from being forcefully rotated with therotation of the rear wheels.

[0394] When it is desired to increase riding performances such as ondifferences in level or cavities in road and acceleration ability, theelectric motor 2129 is rotated to provide a four-wheel driven state tosend drive power to the rear wheels with the one-way clutch 805 inforward running or with both the one-way clutch 805 and the on-offclutch 807 in backward running.

[0395] Cancellation of engagement of the dog clutch 811 is, as describedabove, accelerated by the cam thrust force of the cam angle and thebiasing force of the return spring 815.

[0396] In addition, the controller 2133, when canceling engagement ofthe dog clutch 811, changes the number of rotation of the drive electricmotor 2129 in accordance with the operation method of the embodiment, orchanges the rotational direction to give appropriate vibration to themating teeth 819 and 821 to reduce its frictional resistance.

[0397] The cam thrust force 329, the biasing force and the vibrationgiven to the mating teeth 819 and 821 provides cancellation ofengagement of the dog clutch 811 with significantly quick response.

[0398] Further, oil is flown in from an oil sump of a casing 9 to thedifferential case 223 via oil grooves of the opening and the boss parts259 and 261 to sufficiently lubricate/cool engaging parts of gears ofthe differential mechanism 227, the one-way clutch 805, the dog clutch811 and other components.

[0399] The differential case 223 and the rotation case 809 are providedwith oil flow paths 827 and 829, respectively, which are communicatedwith the one-way clutch 805, to form a back and forth path through theone-way clutch 805.

[0400] When the differential case 223 is in a stopped state, oil issupplied from the oil path 827 on the differential case 223 sideimmersed in the oil sump to the one-way clutch 805. When thedifferential case 223 is rotated, the resultant centrifugal forcesupplies inside oil from the oil path 829 of the rotation case 809 tothe one-way clutch 805, which oil is further emitted from the oil path827 to the outside to sufficiently lubricate/cool the one-way clutch805.

[0401] The transmission system 801 of drive power of the electric motor2129 is thus constituted.

[0402] As described above, when the vehicle runs forward, the powertransmission system 801 rotates the electric motor 2129 to drive therear wheels via the one-way clutch 805, and stops rotation of theelectric motor 2129 to disconnect the motor 2129 from the rear wheelswith the interruption function of the one-way clutch 805, thereby toprotect the electric motor 2129 from rotation of the rear wheels.

[0403] The power transmission system 801 has like effects to those ofthe power transmission system 1 except for the effects produced bydisposing the on-off clutch 5 in the speed-reducing mechanism, using amulti-plate clutch for the on-off clutch and using the gear pump 93 forlubrication.

[0404] In addition, the one-way clutch 805 does not cause rotationresistance such as dragging torque at the cancellation of itsconnection, improving fuel efficiency when rotation of the electricmotor 2129 is stopped (in a two-wheel driven state) and the durabilityof the electric motor 2129.

[0405] The one-way clutch 805 eliminates the need for an operationmechanism and a control mechanism, and also provide large capacity evenwith a compact size and light weight. Consequently the powertransmission system 801 has the more-simplified structure, lower cost,lighter weight, more compact size and better vehicle-mountability andcan handle larger drive power.

[0406] The actuator 813 can be hydraulic.

Ninth Embodiment

[0407] With reference to FIG. 15, description is made of a transmissionsystem 901 of drive power of an electric motor 2129 according to theninth embodiment of the invention and a method of operation thereof.

[0408] The power transmission system 901 has features of the 1^(st),2^(nd), 6^(th), 7^(th)8^(th), 9^(th) and 16^(th) aspects of theinvention and the operating method has features of the 18^(th) and19^(th) aspects of the invention. Note the terms “left” and “right” meanthose of a vehicle equipped with the power transmission system 901, andthose in FIG. 15. Like reference numerals are given to members havinglike functions as those of the power transmission systems 1, 201, 301,401, 501, 601, 701 and 801 according to the 1^(st), 2^(nd), 3^(rd),4^(th), 5^(th), 6^(th), 7^(th) and 8^(th) embodiments of the invention.Those members with like functions are not described to avoid redundancy.

[0409] The power transmission system 901 includes a speed-reducingmechanism 3, a two-way clutch 903 (as a clutch), a rear differential 7,a controller 2133, etc.

[0410] The two-way clutch 903 is constituted with an outer holder 905fixed to an outer shaft 37, an inner holder 909 disposed between theouter holder 905 and an inner shaft 39 and supported via ball bearings907 on the inner shaft 39, a switching knob 913 pressed against theinner holder 909 by a disc spring 911, a plurality of sprags, etc.

[0411] The outer and inner holders 905 and 907 have a plurality ofcircumferentially equi-spaced cutouts with the sprags disposed thereinfor outer and inner end parts being in contact with the outer shaft 37and the inner shaft 39, respectively.

[0412] An end of the switching knob 913 is engaged with a recess 915 ofa gear casing 11. Rotation of the outer shaft 37 generates relativerotation between the inner holder 909 coupled to a stationary side(casing 9) via the switching knob 913 biased by the disc spring 911 andthe outer holder 905 fixed to the outer shaft 37. The sprags areinclined in the relative rotational direction to provide a standby statefor drive power transmission.

[0413] When the outer shaft 37 is rotated in the opposite direction, therelative rotation is in the opposite direction. The sprags are inclinedin this direction to provide a standby state for transmitting drivepower in the opposite direction.

[0414] In each standby state, when the outer shaft 37 (electric motor2129) rotates before the inner shaft 39 (rear wheels) does, the spragsare locked to the outer shaft 37 and the inner shaft 39 to make thetwo-way clutch 903 connected, whereby drive power of the electric motor2129 is transmitted to the rear wheels.

[0415] On the contrary, when the inner shaft 39 (rear wheels) rotatesbefore the outer shaft 37 (electric motor 2129) does, the sprags aredisengaged from the outer shaft 37 and the inner shaft 39 to cancel theconnection of the two-way clutch 903, whereby the electric motor 2129 isdisconnected from the rear wheels.

[0416] The controller 2133 rotates the electric motor 2129 when thevehicle starts moving. When the electric motor 2129 is rotated,preceding rotation of the outer shaft 37 establishes connection of thetwo-way clutch 903 in the standby state for transmitting drive power inthe advancing direction. The electric motor 2129 drives the rear wheelsto assist drive power of the engine.

[0417] When the vehicle is accelerated to a prescribed speed, thecontroller 2133 stops rotation of the electric motor 2129.

[0418] The stopping of rotation of the electric motor 2129 cancels theconnection of the two-way clutch 903 through preceding rotation of theinner shaft 39 associated with rotation of the rear wheels.

[0419] When a rollback phenomenon is produced while the vehicle drivesup on a grade in a four-wheel driven state, the controller 2133 reversesthe rotation of the electric motor 2129 to change the two-way clutch 903to be on standby for the backing direction.

[0420] In the standby state for the backing direction, precedingrotation of the rear wheels caused by the rollback cancel the connectionof the two-way clutch 903.

[0421] Thus, the canceling of connection of the two-way clutch 903disconnects the electric motor 2129 from the rear wheels to be releasedfrom being forcefully rotated by rotation of the rear wheels.

[0422] When it is desired to increase drive torque while running toimprove riding performances such as on differences in level or cavitiesin road and acceleration ability, the electric motor 2129 is rotated toprovide the four-wheel driven state.

[0423] In the case of back running, the two-way clutch 903 is on standbyfor the backing direction. When the vehicle starts moving, the electricmotor 2129 is protected from rotation of the rear wheels like when thevehicle advances, running down on a grade with reduced frictionresistance.

[0424] When it is desired to accelerate canceling connection of thetwo-way clutch 903, the controller 2133 changes the number of rotationof the drive electric motor 2129 according to the operation method ofthis embodiment or changes the direction of rotation to give appropriatevibration to the two-way clutch 903, thereby to facilitate thecancellation of lock of the sprags to the outer shaft 37 and the innershaft 39.

[0425] Accordingly, connection of the two-way clutch 903 is cancelledwith significantly quick response.

[0426] The outer shaft 37 is provided with an oil flow path 917. Theinner shaft 39 is provided with oil flow paths 919 and 921. These pathsconstitute a back and forth path through the two-way clutch 903.

[0427] When the outer shaft 37 is stationary, oil is supplied from theoil path 917 of the outer shaft 37 immersed in an oil sump to thetwo-way clutch 903. Centrifugal force generated by rotation of the outershaft 37 supplies oil to the two-way clutch 903 through the oil paths919 and 921, and emits it from the oil path 917 to the outside tosufficiently lubricate/cool the two-way clutch 903.

[0428] Thus the transmission system 901 of drive power of the electricmotor 2129 is constituted.

[0429] The use of the two-way clutch 903 in the power transmissionsystem 901 as described above provides a protection for the electricmotor 2129 from rotation of the rear wheels when the vehicle runs bothforward and backward.

[0430] Further, the use of the two-way clutch 903 protects the electricmotor 2129 and other elements from being affected by a rollback.

[0431] Further, the fact that it is needless to provide another clutchfor back running provides a simplified structure, low cost, lightweight, compact size and good vehicle-moutability.

[0432] Furthermore, in this embodiment, the on-off clutch 5 is providedat a third shaft closest in the speed-reduction mechanism 3 to thedifferential system 7, so that the on-off clutch 5 can be disposedwithin the projection region of larger components such as a ring gear 31of the differential system 7 to make the entire system compact.

[0433] In addition, the power transmission system 901 has like effectsto those of the power transmission system 801 of the eighth embodiment.

Tenth Embodiment

[0434] With reference to FIG. 16, description is made of a transmissionsystem 1001 of drive power of an electric motor 2129 according to thetenth embodiment of the invention and a method of operation thereof.

[0435] The power transmission system 1001 has features of the 1^(st),2^(nd), 8^(th), 12^(th), and 19^(th) aspects of the invention, and theoperating method has features of the 21^(st) and 22^(nd) aspects of theinvention. Note the terms “left” and “right” mean those of a vehicleequipped with the power transmission system 1001, and those in FIG. 16.Like reference numerals are given to members having like functions asthose of the power transmission systems 1, 201, 301, 401, 501, 601, 701,801 and 901 according to the 1^(st), 2^(nd), 3^(rd), 4^(th), 5^(th),6^(th), 7^(th), 8^(th), 9^(th) and 10^(th) embodiments of the invention,respectively. Those members with like functions are not described toavoid redundancy.

[0436] The power transmission system 1001 includes a speed-reducingmechanism 3, a rear differential 1003, a two-way clutch 1005 (as aclutch), a controller 2133, etc.

[0437] The rear differential 1003 has a differential case 223, arotation case 1007, and a bevel gear-type differential mechanism 227.

[0438] The rotation case 1007 is supported via ball bearings 1009 on theinternal periphery of the differential case 223. A pinion shaft 237 ofthe differential mechanism 227 is engaged with the rotation case 1007 tobe fixed.

[0439] The two-way clutch 1005 is disposed between the rotation case1007 and the differential case 223. When the connection of the two-wayclutch 1005 is established, the drive force of an electric motor 2129which is reduced in the speed-reducing mechanism 3 is transmitted fromthe differential mechanism 227 to rear wheels. When the connection iscanceled, the electric motor 2129 is disconnected from the rear wheels.

[0440] The two-way clutch is constituted with an outer holder 1011 fixedto the differential case 223, an inner holder 1015 disposed between theouter holder 1011 and the rotation case 1007 and supported via ballbearings 1013 on the differential case 223, a switching knob 1019pressed against the inner holder 1015 by a disc spring, a plurality ofsprags, etc.

[0441] As in the two-way clutch 903 (ninth embodiment), the outer andinner holders 1011 and 1015 have a plurality of circumferentiallyequi-spaced cutouts with the sprags disposed therein for outer and innerend parts being in contact with the differential case 223 and therotation case 1007, respectively.

[0442] An end of the switching knob 1019 is engaged with a recess 1021of a gear casing 11. Rotation of the differential case 223 generatesrelative rotation between the inner holder 1015 coupled to a stationaryside (casing 9) via the switching knob 1019 biased by the disc spring1017 and the outer holder 1011 on the differential case 223 side. Thesprags are inclined in the relative rotational direction to provide astandby state for drive power transmission.

[0443] When the differential case 223 is rotated in the oppositedirection, the relative rotation is in the opposite direction. Thesprags are inclined in this direction to provide a standby state fortransmitting drive power in the opposite direction.

[0444] In each standby state, when the differential case 223 (electricmotor 2129) rotates before the rotation case 1007 (rear wheels) does,the sprags are locked to the differential case 223 and the rotation case1007 to make the two-way clutch 1005 connected, whereby drive power ofthe electric motor 2129 is transmitted to the rear wheels.

[0445] On the contrary, when the rotation case 1007 (rear wheels)rotates before the differential case 223 (electric motor 2129) does, thesprags are disengaged from the differential case 223 and the rotationcase 1007 to cancel the connection of the two-way clutch 1005, wherebythe electric motor 2129 is disconnected from the rear wheels.

[0446] The controller 2133 rotates the electric motor 2129 when thevehicle starts moving. The rotation of the electric motor 2129 connectsthe two-way clutch 1005 in the standby state for transmitting drivepower in the advancing direction, and the drive power of the electricmotor 2129 is transmitted to the rear wheels.

[0447] When the vehicle is accelerated to a prescribed speed, thecontroller 2133 stops rotation of the electric motor 2129.

[0448] The stopping of rotation of the electric motor 2129 cancels theconnection of the two-way clutch 1005 through the rotation of the rearwheels.

[0449] When a rollback phenomenon is produced when the vehicle drives upon a grade in a four-wheel driven state, the controller 2133 reversesthe rotation of the electric motor 2129 to change the two-way clutch1005 to be on standby for the backing direction.

[0450] In the standby state for the backing direction, the precedingrotation of the rear wheels caused by the rollback cancel the connectionof the two-way clutch 1005.

[0451] Thus the canceling of the connection of the two-way clutch 1005disconnects the electric motor 2129 from the rear wheels to be releasedfrom being forcefully rotated by the rotation of the rear wheels.

[0452] When it is desired to increase drive torque while running toimprove performance in running over steps, bumps or potholes andacceleration, the electric motor 2129 is rotated to provide thefour-wheel driven state.

[0453] In the case of back running, the two-way clutch 1005 is onstandby for the backing direction. When the vehicle starts moving, theelectric motor 2129 is protected from rotation of the rear wheels likewhen the vehicle advances, running down on a grade with reduced frictionresistance.

[0454] When it is desired to accelerate the canceling of connection ofthe two-way clutch 1005, the controller 2133 changes the number ofrotation of the drive electric motor 2129 according to the operationmethod of this embodiment or changes the direction of rotation to giveappropriate vibration to the two-way clutch 1005, thereby to facilitatethe cancellation of lock of the sprags to the differential case 223 andthe rotation case 1007.

[0455] Accordingly, the connection of the two-way clutch 1005 iscancelled with significantly quick response.

[0456] The differential case 223 has an opening 1023, and bosses 259 and261 with oil grooves through which oil is flown in or out of the case223. The flown-in oil sufficiently lubricate/cool engaging parts ofgears of the differential mechanism 227, the two-way clutch 1005 and theball bearings 1009 with the rotation of the differential case 223.

[0457] The differential case 223 is provided with an oil flow path 1025.The rotation case 1007 is provided with an oil flow path 1027. Thesepaths constitute a back and forth path through the two-way clutch 1005.

[0458] When the differential case 223 is stationary, oil is suppliedfrom the oil path 1025 of the differential case 223 immersed in an oilsump to the two-way clutch 1005. Centrifugal force generated by therotation of the differential case 223 supplies inside oil to the two-wayclutch 1005 through the oil path 1027, and emits it from the oil path1025 to the outside to sufficiently lubricate/cool the two-way clutch1005.

[0459] Thus the transmission system 1001 of the drive power of theelectric motor 2129 is constituted.

[0460] The use of the two-way clutch in the power transmission system1001 as described above provides a protection for the electric motor2129 from the rotation of the rear wheels when the vehicle runs bothforward and backward, resulting in similar effects to those of the powertransmission system 901 in the ninth embodiment.

[0461] Eleventh Embodiment With reference to FIG. 17, description ismade of a transmission system 1101 of drive power of an electric motor2129 according to the eleventh embodiment of the invention and a methodof operation thereof.

[0462] The power transmission system 1101 has features of the 1^(st),2^(nd), 8^(th), 12^(th) and 20^(th) aspects of the invention, and theoperating method has features of the 21^(st) and 22^(nd) aspects of theinvention. Note the terms “left” and “right” mean those of a vehicleequipped with the power transmission system 1101, and those in FIG. 17.Like reference numerals are given to members having like functions asthose of the power transmission systems 1, 201, 301, 401, 501, 601, 701,801, 901, and 1001 according to the 1^(st), 2^(nd), 3^(rd), 4^(th),5^(th), 6^(th), 7^(th), 8^(th), 9^(th), 10^(th) and 11^(th) embodimentsof the invention, respectively. Those members with like functions arenot described to avoid redundancy.

[0463] The power transmission system 1101 includes a speed-reducingmechanism 3, a rear differential 1103, a centrifugal clutch 1105 (as aclutch), a controller 2133, etc.

[0464] The rear differential 1103 has a differential case 223, arotation case 1107 and a bevel gear-type differential mechanism 227.

[0465] The rotation case 1107 is disposed rotatably on the internalperiphery of the differential case 223. A pinion shaft 237 of thedifferential mechanism 227 is engaged with the rotation case 1107 andfixed with a snap ring 1109.

[0466] The centrifugal clutch 1105 is disposed between a left-side gear241 of the differential mechanism 227 and the differential case 223, andhas engaging holes 1111 and 1113 provided in the side gear 241 and thedifferential case 223, respectively, in the centrifugal force direction,engaging member 115 engaged with the engagement hole 1111 in the sidegear 241, a coil spring 1117 biasing the engaging member 1115 to theengaging hole 1113 in the differential case 223 against centrifugalforce, etc.

[0467] When the rear differential 1103 is stationary, the biasing forceof the coil spring 1117 engages the engagement member 1115 with theengagement hole 1113 to establish connection of the centrifugal clutch1105.

[0468] At the connection of the centrifugal clutch 1105, the side gear241 is locked to the differential case 223, the differential case 223and the differential mechanism 227 (the rotation case 1007 rear wheels)are connected, and the drive power of the electric motor 2129 istransmitted from the differential mechanism 227 to the rear wheels.

[0469] Differential rotation of the differential mechanism 227 is alsolocked.

[0470] When the rear differential 1103 is rotated, the resultantcentrifugal force applied to the engaging member 1115 deforms the coilspring 1117, the engaging member 1115 is moved to cancel its engagementwith the engaging hole 1113, and the connection of the centrifugalclutch 1 10S is canceled.

[0471] At the cancellation of the connection of the centrifugal clutch1105, the side gear 241 is released to rotate, the connection betweenthe differential mechanism 227 and the differential case 223 iscancelled, the electric motor 2129 is disconnected from the rear wheels,and the differential lock of the differential mechanism 227 is released.

[0472] The coil spring 1117 has a property (biasing force) of cancelingthe connection of the centrifugal clutch 1105 when vehicle speed isincreased to a prescribed level.

[0473] The controller 2133 rotates the electric motor 2129 when thevehicle starts moving. While the vehicle is accelerated to a prescribedspeed, the electric motor 2129 drives the rear wheels via thecentrifugal clutch 1105 to assist the drive power of the engine,improving properties in starting and acceleration and also improvingperformance in running over steps, bumps or potholes.

[0474] Further, differential motions of the differential mechanism 227is locked as described above, which fact improves properties instarting, acceleration and performance in running over steps, bumps orpotholes on roads with reduced friction resistance.

[0475] When the connection of the centrifugal clutch 1105 is cancelledat a prescribed vehicle speed, the controller 2133 sequentially stopsthe rotation of the electric motor 2129.

[0476] In this state, the electric motor 2129 is disconnected from therear wheels by the centrifugal clutch 1105 and is thus prevented frombeing forcefully rotated by rotation of the rear wheels.

[0477] At the time of back running, connection and disconnection of thecentrifugal clutch 1105 can, as in the forward running, start andaccelerate the vehicle or disconnect the electric motor 2129 from therear wheels.

[0478] When it is desired to accelerate the canceling of connection ofthe centrifugal clutch 1105, the controller 2123 changes the number ofrotation of the drive electric motor 2129 or changes the rotationaldirection in accordance with the operation method of this embodiment, toprovide appropriate vibration to the centrifugal clutch 1105, thereby tofacilitate disengagement between the engaging member 1115 and theengaging hole 1113.

[0479] Accordingly, the cancellation of connection of the centrifugalclutch 1105 is performed with significantly quick response.

[0480] The differential case 223 has an opening 1119 and bosses 259 and261 with oil grooves through which oil is flown in or out of the case223. The flown-in oil sufficiently lubricates/cools engaging parts ofgears of the differential mechanism 227 with the rotation of the case223, and lubricates sliding parts of the engaging member 1115 and theengaging hole 1113 of the centrifugal clutch 1105, thereby to furtheraccelerate the cancellation of the connection of the centrifugal clutch1105.

[0481] Thus the transmission system 1101 of drive power of the electricmotor 2129 is constituted.

[0482] In the power transmission system 1101, the electric motor 2129is, as described above, disconnected from the rear wheels by thecentrifugal clutch 1105 when necessary.

[0483] Further, the power transmission system 1101 provides similareffects to those of the power transmission system 1 except for theeffects obtained by disposing the clutch 5 between the speed-reducingmechanisms, using a multi-plate clutch for the clutch 5 and using thegear pump 93 for lubrication.

[0484] In addition, the cancellation of connection of the centrifugalclutch 1105 does not cause rotation resistance such as dragging torque,improving fuel efficiency at the time of stopping rotation of theelectric motor 2129 (two wheel driven) and durability.

[0485] Further, the centrifugal clutch 1105 eliminates the need for anoperating mechanism and a control mechanism and provides large capacityeven with its small size and light weight. This makes the powertransmission system 1101 have easy structure, low cost, light weight,compact size, good vehicle mountability and an ability of handling largedrive power.

[0486] The centrifugal clutch can be disposed between the differentialcase 223 and the rotation case 1107 instead of between the differentialcase 223 and the side gear 214.

[0487] In this case, the differential mechanism 227 can differentiallydistribute drive power of the electric motor 2129 to the rear wheels.

[0488] Twelfth Embodiment

[0489] With reference to Fig.18 and Fig.19, description is made of atransmission system 1201 of drive power of an electric motor 2129according to the twelfth embodiment of the invention and a method ofoperation therefor.

[0490] The power transmission system 1201 has features of the 1^(st),2^(nd), 3^(rd), 4^(th), 5^(th), 8^(th), 9^(th), 10^(th) , 11^(th),12^(th), 16^(th) and 17^(th) aspects of the invention, and the operatingmethod has features of the 21^(st) and 22^(nd) aspects of the invention.Note the terms “left” and “right” mean those of a vehicle equipped withthe power transmission system 1201, and those in FIG. 18. Like referencenumerals are given to members having like functions as those of thepower transmission systems 1, 201, 301, 401, 501, 601, 701, 801, 901,1001 and 1101 according to the 1^(st), 2^(nd), 3^(rd), 4^(th), 5^(th),6^(th), 7^(th), 8^(th), 9^(th), 10^(th), 11^(th), 12^(th), 13^(th) and14^(th) embodiments of the invention, respectively. Those members withlike functions are not described to avoid redundancy.

[0491] The power transmission system 1201 includes a speed-reducingmechanism 1203, a rear differential 1205, an on-off clutch 1207 (as aclutch), a gear pump 1209 (as a trochoid pump), a controller 2133, etc.

[0492] The rear differential 1205 and the on-off clutch 1207 aredisposed in a reversed manner in the right and left direction of that ofthe rear differential 405 and the on-off clutch 407 of the fourthembodiment (FIG. 6), and have the same functions.

[0493] The speed-reducing mechanism 1203 is constituted with three-stagereduction gear sets. A reduction gear set 1211 of a planetary gear typeis in the first stage. Reduction gear sets 17 and 19 are in the secondand third stages.

[0494] The reduction gear set 1211 of the planetary gear type is, asshown in FIG. 19, constituted with an internal gear 1213, three piniongears 1215 engaged with the internal gear 1213, a sun gear 1217 engagedwith the pinion gears 1215, etc.

[0495] The internal gear 1213 is welded to a gear casing 11. The piniongears 1215 are disposed circumferentially at the same intervals.

[0496] The pinion gears 1215 are supported on pinion shafts 1219. Thepinion shafts 1219 are supported at their both ends with right and leftpinion carriers 1221 and 1223. The pinion carriers 1221 and 1223 areintegrated at coupling parts 1225.

[0497] The left pinion carrier 1221 is welded to a second shaft 35 ofthe reducing gear set 17.

[0498] The sun gear 1217 is formed at a first hollow shaft 1227. Thefirst shaft 1227 is supported on its left end on the internal peripheryof the second shaft 35 via needle bearings 1229 and is supported on itsright end on the internal periphery of the right pinion carrier 1223 viaball bearings 1231.

[0499] To the first shaft 1227, an output axis 1233 of an electric motor2129 for driving rear wheels is spline-coupled. An oil seal 1235 isdisposed between the first shaft 1227 and the gear casing 11 to preventthe leakage of oil. The first shaft 1227 is sealed at its internalperiphery with a lid member 1237 to prevent the leakage of oil and theintrusion of foreign material.

[0500] When the electric motor 2129 is rotated, the resultant drivepower is input from the sun gear 1217 to the reduction gear set 1211 ofa planetary gear, and reduced by the rotation and revolution of thepinion gears 1215, and further reduced by the reduction gear sets 17 and19 to rotate a differential case 223 of the rear differential 1205.

[0501] When it is desired to increase drive torque of the vehicle, thecontroller 2133 rotates the electric motor 2129 to establish theengagement of a dog clutch 411 of the on-off clutch 1207, thereby toprovide a four-wheel driven state.

[0502] When a two wheel driven state or a rollback phenomenon isproduced, the rotation of the electric motor 2129 is stopped to cancelthe engagement of the dog clutch 411, thereby to disconnect the electricmotor 2129 from rear wheels to prevent it from being unnecessarilyrotated by the rotation of the rear wheels.

[0503] The gear pump 1209 is disposed between the gear casing 11 and thesecond shaft 35 to be driven by the rotation of the second shaft 35.

[0504] The second shaft 35, the pinion carrier 1221 and the pinion gear1219 are provided with oil paths 1239, 1241, 1243 and 1245. The oil path1239 of the second shaft 35 is sealed with a lid member 1247. The oilpath 1243 of the pinion gear 1219 is sealed with a ball 1249 pressedfitted therein. When the gear pump 1209 is driven, oil is sucked up froman oil sump of a casing 9 to be sent to the reduction gear set 1211through the oil paths 1239, 1241, 1243 and 1245.

[0505] The rotation of the second shaft 35 generates centrifugal pumpeffects in a diameter-enlarged part 1251 formed in the oil path 1239,accelerating the transfer of the oil.

[0506] The oil sent to the reduction gear set 1211 sufficientlylubricates/cools engaging parts of the gears 1213, 1215 and 1217, asupported part of the pinion gear 1215, the needle bearings 1229 and theball bearings 1231.

[0507] An oil seal 1253 is disposed between the third shaft 213 and thegear casing 11 to prevent the leakage of oil.

[0508] Thus the transmission system 1201 of the drive power of theelectric motor 2129 is constituted.

[0509] In the power transmission system 1201, the electric motor 2129 isdisconnected from the rear wheels by the on-off clutch 1207 whennecessary to be prevented from being unnecessary rotated by the rotationof the rear wheels as described above.

[0510] The power transmission system 1201 has similar effects to thoseof the power transmission system 401 of the fourth embodiment of theinvention.

[0511] In addition, the power transmission system 1201 has the reductiongear set 1211 of a planetary gear as the first-stage reductionmechanism, in which the first shaft 1227 is disposed concentrically withthe second shaft 35, thereby having a three-shaft structure with oneshaft less than other embodiments having a four-shaft structureincluding the rear differential, resulting in a largely compact size andan improved vehicle-mountability.

[0512] The third reduction gear set 19 (the final reduction gear set)and the reduction gear set 17 in the previous stage of the finalreduction gear set 19 are disposed adjacent to each other in the axialdirection, which allows making them compact in the axial direction.Further, the supporting span of the reduction gears can be short forproper meshing of bearings of the gears, which results in reducedvibration and improved durability.

[0513] The reduction gear set 17 in the previous stage of the finalreduction gear set 19 is disposed on one side of the final reductiongear set 19 in the axial direction, and the differential system isdisposed on the other side of the final reduction gear set 19 in theaxial direction. Thus the casing 9 in which integrally mounted are thefinal reduction gear set and the differential system can have anunbalance-suppressed weight in the wheel axle direction (the transversedirection).

[0514] The clutch is disposed coaxially adjacent to and outside of thedifferential system in the axial direction. This also can suppressunbalance of the casing 9 in the wheel axle direction (the transversedirection). Further the clutch can be set with little restriction ininterference with the peripheral members, which improves degree offreedom of design such as the size and the shape of the clutch andsetting conditions of an actuator.

[0515] Thirteenth Embodiment

[0516] With reference to FIG. 20, description is made of a transmissionsystem 1301 of drive power of an electric motor 2129 according to thethirteenth embodiment of the invention and a method of operationthereof.

[0517] The power transmission system 1301 has features of the 1^(st),2^(nd), 3^(rd), 4^(th), 5^(th), 8^(th) , 12^(th), 16^(th) and 17^(th)aspects of the invention, and the operating method has features of the21^(st) and 22^(nd) aspects of the invention. Note the terms “left” and“right” mean those of a vehicle equipped with the power transmissionsystem 1301, and those in FIG. 20. Like reference numerals are given tomembers having like functions as those of the power transmission systems1, 201, 301, 401, 501, 601, 701, 801, 901, 1001, 1101 and 1201 accordingto the 1^(st), 2^(nd), 3^(rd), 4^(th), 5^(th), 6^(th), 7^(th), 8^(th),9^(th), 10^(th), 11^(th) and 12^(th) embodiments of the invention,respectively. Those members with like functions are not described toavoid redundancy.

[0518] The power transmission system 1301 includes a speed-reducingmechanism 1203, a rear differential 1205, a connection/disconnectionclutch 1207 (as a clutch), a screw pump 1303, a controller 2133, etc.

[0519] The screw pump 1303 has a shaft 1305 fixed to a gear casing 11, aspiral groove 1307 provided on the shaft 1305 and a oil path 1239 of asecond shaft 35. The shaft 1305 is disposed concentrically with the oilpath 1239.

[0520] With rotation of the second shaft 35, oil in the oil path 1239 isrotated because of its viscosity. The rotated oil moves along the spiralgroove 1307, sucking oil in a oil sump as shown by arrows 1309, to besent to a reduction gear set 1211 through oil paths 1239, 1241, 1243 and1245.

[0521] The oil sent to the reduction gear set 1211 sufficientlylubricates/cools engaging parts of gears 1213, 1215 and 1217, supportedpart of the pinion gears 1215 and the bearings 1229 and 1231.

[0522] Since a vehicle running backward is usually at a significantlylow speed with small load on the reduction gear set 1211, whicheliminates the need for an especially large lubrication mechanism.

[0523] The transmission system 1301 of drive power of the electric motor2129 is constituted in this manner.

[0524] The power transmission system 1301 provides similar effects tothose of the power transmission system 1201 of the twelfth embodiment.

[0525] In addition, the screw pump 1303 has a simple and low-coststructure and is easy to assemble. Thus, use of the screw pump 1303allows the power transmission system 1301 to have a simple and low-coststructure and to be easy to assemble.

[0526] Fourteenth Embodiment

[0527] With reference to FIG. 21, description is made of a transmissionsystem 1401 of drive power of an electric motor 2129 according to thefourteenth embodiment of the invention and a method of operationthereof.

[0528] The power transmission system 1401 has features of the 1^(st),2^(nd), 3^(rd), 4^(th), 5^(th), 8^(th), 12^(th), 16^(th) and 17^(th)aspects of the invention, and the operating method has features of the21^(st) and 22^(nd) aspects of the invention. Note the terms “left” and“right” mean those of a vehicle equipped with the power transmissionsystem 1401, and those in FIG. 21. Like reference numerals are given tomembers having like functions as those of the power transmission systems1, 201, 301, 401, 501, 601, 701, 801, 901, 1001, 1101, 1201 and 1301according to the 1^(st), 2^(nd), 3^(rd) , 4^(th), 5^(th), 6^(th),7^(th), 8^(th), 9^(th), 10^(th), 11^(th), 12^(th) and 13^(th)embodiments of the invention, respectively. Those members with likefunctions are not described to avoid redundancy.

[0529] The power transmission system 1401 includes a speed-reducingmechanism 1203, a rear differential 1205, a connection/disconnectionclutch 1207 (as a clutch), a centrifugal pump 1403, a controller 2133,etc.

[0530] A second shaft 35 of the speed-reducing mechanism 1203 issupported at its left end with a gear casing 11 via a taper rollerbearing 1405. The taper roller bearing 1405 constitutes the centrifugalpump 1403.

[0531] When the second shaft 35 rotates, an inner race 1407 and a roller1409 of the taper roller bearing 1405 are rotated. The resultantcentrifugal force causes oil to hit upon an oblique surface of an outerrace 1411. The oil moves as shown by arrows 1413, sucking oil in a oilsump to be sent to the reduction gear set 1211 through oil paths 1239,1241, 1243 and 1245.

[0532] This oil transfer is speeded up by centrifugal pump effects of adiameter-enlarged part 1251 with the rotation of the second shaft 35.

[0533] The oil sent to the reduction gear set 1211 sufficientlylubricates/cools engaging parts of gears 1213, 1215 and 1217, supportedpart of the pinion gears 1215 and bearings 1229 and 1231.

[0534] The centrifugal pump 1403 functions in the same manner in bothdirections of rotation of the second shaft 35. Thus the reduction gearset 1211 is sufficiently lubricated/cooled in both forward running andbackward running of a vehicle.

[0535] The transmission system 1401 of drive power of the electric motor2129 is constituted in this manner.

[0536] The power transmission system 1401 provides similar effects tothose of the power transmission system 1201 of the twelfth embodiment.

[0537] In addition, the fact that the taper roller bearing 1405 is usedfor the centrifugal pump 1403 realizes the power transmission system1401 without complicating structure and assembling operation andincreasing cost and weight.

[0538] The above embodiments show examples of application to an electricautomobile with the engine as a main drive source and the electric motor2129 as an auxiliary drive source. However, the transmission system ofdrive power of the electric motor 2129 of this invention can also beused for a vehicle with the electric motor 2129 as a main drive source.

[0539] Further, the differential system can be any one such as aplanetary gear differential system, a differential system with anoutput-side gear coupled with a pinion gear slidably held in anaccommodation hole of a differential case and a differential system witha worm gear, instead of the bevel gear-type differential system of theembodiments.

[0540] While preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes, and it is to be understood that changes and variations may bemade without departing from the spirit or scope of the following claims.

What is claimed is:
 1. A power transmission system comprising: a speedreducing mechanism for speed-reducing drive power of an electric motor;a differential apparatus for distributing speed-reduced drive power toaxle ends; and a clutch configured for interruptive transmission ofdrive power between the speed-reducing mechanism and the differentialapparatus.
 2. A power transmission system according to claim 1, furthercomprising: a main drive power source; and the electric motor used as anauxiliary drive power source relative to the main drive power source. 3.A power transmission system according to claim 1, wherein thespeed-reducing mechanism comprises a plurality of reduction gear setsincluding a first reduction gear set for inputting thereto drive powerfrom the electric motor, the first reduction gear set comprising aplanetary gear.
 4. A power transmission system according to claim 3,wherein the speed-reducing mechanism is provided with an oil pump forsupplying lubricant to the planetary gear.
 5. A power transmissionsystem according to claim 4, wherein the oil pump is provided on a lidside of a case.
 6. A power transmission system according to claim 1,wherein the speed-reducing mechanism comprises a plurality of reductiongear sets, and the clutch is disposed in a power transmission path ofthe speed-reducing mechanism.
 7. A power transmission system accordingto claim 6, wherein the speed-reducing mechanism and the differentialapparatus are neighbored to each other, and the clutch is coaxiallyprovided to one of the plurality of reduction gear sets of thespeed-reducing mechanism that is nearest to the differential apparatus.8. A power transmission system according to claim 1, wherein thespeed-reducing mechanism and the differential apparatus are integrallyarranged in a casing.
 9. A power transmission system according to claim8, wherein a final reduction gear set and a previous reduction gear setrelative thereto are axially neighbored to each other.
 10. A powertransmission system according to claim 9, wherein the previous reductiongear set is disposed on an axially one side of the final reduction gearset, and the differential apparatus is disposed on an axially oppositeside of the final reduction gear set.
 11. A power transmission systemaccording to claim 10, wherein the clutch is coaxially neighbored, at anaxially outer side, to the differential apparatus.
 12. A powertransmission system according to claim 7, wherein the plurality ofreduction gear sets of the speed-reducing mechanism is provided near adifferential center of the differential apparatus.
 13. A powertransmission system according to claim 1, wherein the clutch comprises africtional clutch.
 14. A power transmission system according to claim13, wherein the frictional clutch comprises a multi-plate clutch.
 15. Apower transmission system according to claim 13, wherein the frictionalclutch comprises a cone clutch.
 16. A power transmission systemaccording to claim 1, wherein the clutch comprises a meshing clutch. 17.A power transmission system according to claim 16, wherein the meshingclutch comprises a dog clutch.
 18. A power transmission system accordingto claim 1, wherein the clutch comprises a one-way clutch.
 19. A powertransmission system according to claim 1, wherein the clutch comprises atwo-way clutch in which canceling directions of relative rotations areswitchable.
 20. A power transmission system according to claim 1,wherein the clutch comprises a centrifugal clutch.
 21. An operationmethod for a power transmission system according to claim 16, the methodcomprising the step of canceling connection of the clutch, switching arotating direction of the electric motor, thereby causing a contactportion of the clutch to vibrate so that the contact portion has areduced frictional resistance.
 22. An operation method for a powertransmission system according to claim 16, the method comprising thestep of canceling connection of the clutch, changing a revolution numberof the electric motor so that a contact portion thereof has a reducedfrictional resistance.
 23. An operation method for a power transmissionsystem according to claim 18, the method comprising the step ofcanceling connection of the clutch, switching a rotating direction ofthe electric motor, thereby causing a contact portion of the clutch tovibrate so that the contact portion has a reduced frictional resistance.24. An operation method for a power transmission system according toclaim 18, the method comprising the step of canceling connection of theclutch, changing a revolution number of the electric motor so that acontact portion thereof has a reduced frictional resistance.
 25. Anoperation method for a power transmission system according to claim 19,the method comprising the step of canceling connection of the clutch,switching a rotating direction of the electric motor, thereby causing acontact portion of the clutch to vibrate so that the contact portion hasa reduced frictional resistance.
 26. An operation method for a powertransmission system according to claim 19, the method comprising thestep of canceling connection of the clutch, changing a revolution numberof the electric motor so that a contact portion thereof has a reducedfrictional resistance.
 27. An operation method for a power transmissionsystem according to claim 20, the method comprising the step ofcanceling connection of the clutch, switching a rotating direction ofthe electric motor, thereby causing a contact portion of the clutch tovibrate so that the contact portion has a reduced frictional resistance.28. An operation method for a power transmission system according toclaim 20, the method comprising the step of canceling connection of theclutch, changing a revolution number of the electric motor so that acontact portion thereof has a reduced frictional resistance.